Thursday, August 18, 2011

Mineral C

THE MINERAL CACOXENITE

 

  • Chemistry: Fe24(AlO6)(PO4)17(OH)12 - 75H2O, Hydrated Iron Aluminum Phosphate Oxide Hydroxide.
  • Class: Phosphates
  • Uses: Only as mineral specimens.
  • Specimens

Cacoxenite is a mineral that is commonly an inclusion in quartz, especially amethyst. The inclusions in amethyst often detract from the amethyst as the brown acicular needles dampen the pure purple color to a less desirable brownish hue. The inclusions of cacoxenite will certainly ruin any chance for the host stone to become a gemstone. This is not to say that some specimens of cacoxenite included quartz have no value, for indeed some are actually enhanced with interesting surreal landscaping effects.
Cacoxenite on its own is appreciated as a scarce phosphate mineral and is known from classic phosphate localities. It is often associated with other attractive and rare phosphates and can therefore represent some very nice mineral specimens. These specimens can be quite popular and attractive with a silky luster and a typical yellow-brown color.
The rather daunting formula of cacoxenite, Fe24(AlO6)(PO4)17(OH)12 - 75H2O, can be represented in a more condensed and simpler version, Fe4(PO4)3(OH)3 - 12H2O. This shorter version is what is often used in some references. The shorter version is approximately one sixth of the larger one except for the addition of one aluminum and an adjustment to the number of oxygens and water molecules. This can be demonstrated:
  • Fe24 (AlO6) (PO4)17 (OH)12 - 75H2O
  • The aluminum group occupies a phosphate position in the structure and this can be shown as follows:
  • Fe24 [(AlO6), (PO4)]18 (OH)12 - 75H2O
  • Combine the 6 oxygens to 6 hydrogens from three water molecules to form 6 more OH's:
  • Fe24 [Al, (PO4)]18 (OH)18 - 72H2O
  • Then the formula can be shown as:
  • Fe(6x4) [Al, (PO4)](6x3) (OH)(6x3) - 6x12H2O ;
  • factoring out 6 and ignoring the aluminum gives:
  • 6 x (Fe4 (PO4)3 (OH)3 - 12H2O)

This change requires the loss of three oxygens in order to balance the formula due to the change in charge from one negative 3 phosphate group to the negative 9 aluminum group. Natural cacoxenite contains one aluminum group for every 17 phosphates making the larger formula more accurate, if not less cumbersome.

 

PHYSICAL CHARACTERISTICS:

  • Color is yellow-brown, brown, reddish-yellow, greenish-yellow or yellow.
  • Luster is vitreous to silky.
  • Transparency: Specimens are translucent to transparent.
  • Crystal System is hexagonal.
  • Crystal Habits include acicular radiating crystals often as inclusions, also massive, globular, botryoidal and fibrous tufts.
  • Cleavage is poor.
  • Fracture is fibrous.
  • Hardness is 3 - 4
  • Specific Gravity is approximately 2.3 (below average).
  • Streak is yellow.
  • Associated Minerals include quartz, hematite, strengite, beraunite, rockbridgeite and limonite.
  • Notable Occurrences include Cornwall, England; Sweden; France; Hagendorf, Germany; Antwerp, New York; Pima County, Arizona; Indian Mountain, Alabama and Coon Creek Mine, Polk County, Arkansas, USA.
  • Best Field Indicators are crystal habit, color, associations, density and streak. 

THE MINERAL CALAVERITE

 

  • Chemistry: AuTe2, Gold Telluride.
  • Class: Sulfides
  • Subclass: Tellurides
  • Uses: A very minor ore of gold and tellurium and as mineral specimens.
  • Specimens

Calaverite is an uncommon and much sought after mineral by mineral collectors and those seeking fortunes. Calaverite is one of the few minerals that is an ore of gold, besides native gold itself. It is the most common gold bearing mineral besides native gold. The element gold is typically either found as native gold (in its elemental state), as an alloy with other metals such as silver and copper and as trace amounts in a few minerals. To be an actual significant part of a non-alloyed mineral is really quite uncommon for gold and this makes calaverite a unique mineral indeed.

For some reason gold has an affinity for the element tellurium, which is sometimes found naturally as native tellurium. Tellurium is a semi-metallic element which means that it has some properties of metals but not all or as strongly. This helps provide an explanation for gold's, and other metals such as silver's, attraction to tellurium. Other gold tellurides include sylvanite, (Silver Gold Telluride); kostovite, (Copper Gold Telluride); krennerite, (Silver Gold Telluride); nagyagite, (Gold Lead Antimony Iron Telluride Sulfide) and petzite (Silver Gold Telluride). Calaverite is closely related to sylvanite and differs only in silver content and slightly in hardness, cleavage, color and density. At times the two minerals are only distinguishable with chemical tests.

Crystals of calaverite are unique and of interest to collectors. Typically found as striated prisms that can be twinned causing sharp bends, reticulated individuals and skeletal or arborescent formations. These clusters remind many collectors of writing.

 

 

 

PHYSICAL CHARACTERISTICS:

  • Color is silver white to brassy yellow.
  • Luster is a bright metallic.
  • Transparency: Crystals are opaque.
  • Crystal System: Monoclinic; 2/m
  • Crystal Habits include prismatic to more rarely tabular crystals that are often twinned into sharp bends, reticulated individuals and skeletal or arborescent formations. These are sometimes described as looking like writing. Also found as granular masses.
  • Cleavage is absent.
  • Fracture is conchoidal.
  • Hardness is 2.5 - 3
  • Specific Gravity is approximately 9.1 - 9.3 (very heavy even for metallic minerals).
  • Streak is a yellow gray.
  • Other Characteristics: Crystals tend to be deeply striated parallel to the prominent length.
  • Associated Minerals include gold, quartz, celestite, fluorite, pyrite, nagyagite, sylvanite, krennerite and other rare telluride minerals.
  • Notable Occurrences include Cripple Creek in Teller County, Colorado and Calaveras County (from where it gets its name), California, USA; Nagyag, Romania; Kirkland lake Gold District, Ontario and Rouyn District, Quebec, Canada and Kalgoorlie, Australia.
  • Best Field Indicators are crystal habit, density, softness, color, luster, association with other tellurides and gold and lack of cleavage.

THE MINERAL CALCITE

  

  • Chemistry: CaCO3, Calcium Carbonate
  • Class: Carbonates
  • Group: Calcite
  • Uses: In cements and mortars, production of lime, limestone is used in the steel industry; glass industry, ornamental stone, chemical and optical uses and as mineral specimens.
  • Calcite's Physical Properties
  • Specimens

Calcite, which gets its name from "chalix" the Greek word for lime, is a most amazing and yet, most common mineral. It is one of the most common minerals on the face of the Earth, comprising about 4% by weight of the Earth's crust and is formed in many different geological environments. Calcite can form rocks of considerable mass and constitutes a significant part of all three major rock classification types. It forms oolitic, fossiliferous and massive limestones in sedimentary environments and even serves as the cements for many sandstones and shales. Limestone becomes marble from the heat and pressure of metamorphic events. Calcite is even a major component in the igneous rock called carbonatite and forms the major portion of many hydrothermal veins. Some of these rock types are composed of better than 99% calcite. Why would a collector be interested in such a common mineral? Its extraordinary diversity and beauty!

With calcite so abundant and so widely distributed it is no wonder that it can be so varied. The crystals of calcite can form literally a thousand different shapes by combining the basic forms of the positive rhombohedron, negative rhombohedron, steeply, moderately and slightly inclined rhombohedrons, various scalahedrons, prism and pinacoid to name a few of the more common forms. There are more than 300 crystal forms identified in calcite and these forms can combine to produce the thousand different crystal variations. Calcite also produces many twin varieties that are favorites among twin collectors. There are also phantoms, included crystals, color varieties, pseudomorphs and unique associations. There simply is no end to the varieties of calcite.

There are several varieties of calcite and it would be impossible to describe them all. However there are a few standouts. Possibly the most well known of calcite's varieties is its most common form, the classic scalenohedron or "Dogtooth Spar" as it is sometimes called. This variety appears as a double pyramid or dipyramid, but is actually a distinctly different form. The point of the scalenohedron is sharp and resembles the canine tooth of a dog, hence the name. Beautiful clear colorless or amber-orange examples of this variety are considered classics and outstanding examples come from Pugh Quarry, Ohio; Cornwall, England and Elmwood, Tennessee but the variety is found worldwide.
Not necessarily a variety of calcite, cave formations are certainly a unique aspect of calcite's story. Calcite is the primary mineral component in cave formations. Stalactites and stalagmites, cave veils, cave pearls, "soda straws" and the many other different cave formations that millions of visitors to underground caverns enjoy are made of calcite. It is the fact that calcite is readily dissolved that these formations occur. Overlying limestones or marbles are dissolved away by years and years of slightly acidic ground water to percolate into the caverns below. In fact the caverns themselves may have been the result of water dissolving away the calcite rich rock. As the calcite enriched water enters a relatively dry cavern, the water starts to evaporate and thus precipitate the calcite. The resulting accumulations of calcite are generally extremely pure and are colored if at all, by very small amounts of iron or other impurities.

Mexican onyx is a variety of calcite that is used extensively for ornamental purposes. It is carved into figurines and is so popular that almost every child in the USA owns a small onyx animal or two. Carvings such as vases, bookends, plates, eggs, obilisks, pyramids and statues are all popular. It is not the same onyx as the quartz variety of onyx which is a little more precious (it is used in jewelry) and is banded white and black. To avoid confusion it is best to refer to it as Mexican Onyx. Mexican onyx is banded with multiple orange, yellow, red, tan, brown and white colors that have marble-like texture. The carvings are quite attractive and affordable; a rare combination!

Another variety is the so called "Iceland Spar", which is basically clear cleaved fragments of completely colorless (ice-like) calcite. Originally discovered and named after Eskifjord, Iceland where the calcite is found in basalt cavities. In rock shops around the world, iceland spar is available in large quantities and at affordable prices and are popular among children. Most of today's iceland spar comes from Mexico. The iceland spar displays the classic cleavage form of calcite, the rhombohedron. Iceland spar was and is used for optical equipment and during World War II it was a strategic mineral as it was used for the sighting equipment of bombardiers and gunners. It is iceland spar that best demonstrates the unique property of calcite called double refraction.

  Double refraction occurs when a ray of light enters the crystal and due to calcite's unique optical properties, the ray is split into fast and slow beams. As these two beams exit the crystal they are bent into two different angles (known as angles of refraction) because the angle is affected by the speed of the beams. A person viewing into the crystal will see two images ... of everything. The best way to view the double refraction is by placing the crystal on a straight line or printed word (the result will be two lines or two words). There is only one direction that the beams are both the same speed and that is parallel to the C-axis or primary trigonal axis. Rotation of the crystal will reveal the direction in the crystal that is parallel to the C-axis when the line or word becomes whole again. By contrast, the direction perpendicular to the C-axis will have the greatest separation. The extremely high index of refraction of calcite that causes the easily seen double refraction is also responsible for the interference colors (pastel rainbow colors) that are seen in calcites that have small fractures.

Fluorescence, phosphorescence, thermoluminescence and triboluminescence are other important properties of calcite. Although not all specimens demonstrate these properties, some do quite well and this is diagnostic in some cases. One notable case of fluorescence occurs at Franklin, New Jersey where the massive calcite is enriched in a small amount of manganese and fluoresces a bright red under UV light. Some Mexican iceland spar can fluoresce a nice purple or blue color and unique specimens will even phosphoresce (continue to glow) after the UV source has been removed. Triboluminescence is supposedly a property that should occur in most specimens, but is not easily demonstrated. It occurs when the specimen is struck or put under pressure; in a dark room the specimen should glow when this happens.

The best property of calcite is the acid test. Why? Because calcite always will effervesce (bubble) when even cold weak acids are placed on specimens. Even the cement in sandstones will effervesce assuring the geologist of identification of the cementing mineral. The reason for the bubbling is in the formula below:
CaCO3 + 2H(+1) -------> Ca(+2) + H2O + CO2 (a gas)

The carbon dioxide gas (CO2) is given off as bubbles and the calcium dissolves in the residual water. Any acid, just about, can produce these results, but dilute hydrochloric acid or vinegar are the two recommended acids for this test. Other carbonates such as dolomite or siderite do not react as easily with these acids as does calcite and this leads to differentiating these somewhat similar minerals more readily.

Calcite is intricately tied to carbon dioxide in another way. Since many sea organisms such as corals, algae and diatoms make their shells out of calcite, they pull carbon dioxide from the sea water to accomplish this in a near reverse of the reaction above. This is fortuitous for us, as carbon dioxide has been found to be a green house gas and contributes to the so called "green house gas effect". Environmentally then, calcite is very important and may have been quite important to the successful development of our planet in the past. By pulling carbon dioxide out of the sea water, this biological activity allows more of the carbon dioxide in the air to dissolve in the sea water and thus acts as a carbon dioxide filter for he planet. Environmentalists are now actively engaged in determining if this activity can be increase by human intervention to the point of warding off the "green house gas effect". A significant amount of calcite precipitation in sea water is undoubtedly inorganic, but the exact amount that this contributes is not well known. Calcite and other carbonate minerals are very important minerals in the ocean ecosystems of the world.

Calcite is not the only calcium carbonate mineral. There are no less than three minerals or phases of CaCO3. Aragonite and vaterite are polymorphs (latin for "many shapes") with calcite, meaning they all have the same chemistry, but different crystal structures and symmetries. Aragonite is orthorhombic, vaterite is hexagonal and calcite is trigonal. Aragonite is a common mineral, but is vastly out distanced by calcite which is the more stable mineral at most temperatures and pressures and in most environments. Vaterite on the other hand is extremely scarce and rarely seen. Aragonite will over time convert to calcite and calcite pseudomorphs after aragonite are not uncommon.

Calcite is truly one of the best collection type minerals. There are lots of interesting forms and varieties as well as colorful and beautiful specimens to collect. It is generally easy to identify using its rhomohedral cleavage, reaction to acid and double refraction and makes for a great classroom example of these properties. If it is not the significant mineral on a specimen, it might be an accessory to other wonderful minerals and only enhancing their attractiveness. With its many different forms, environments, associations and colors, a collector could never have all possible combinations of calcite covered.

 

PHYSICAL CHARACTERISTICS OF CALCITE:

  • Color is extremely variable but generally white or colorless or with light shades of yellow, orange, blue, pink, red, brown, green, black and gray. Occasionally iridescent.
  • Luster is vitreous to resinous to dull in massive forms.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is trigonal; bar 3 2/m
  • Crystal Habits are extremely variable with almost any trigonal form possible. Common among calcite crystals are the scalenohedron, rhombohedron, hexagonal prism, and pinacoid. Combinations of these and over three hundred other forms can make a multitude of crystal shapes, but always trigonal or pseudo-hexagonal. Twinning is often seen and results in crystals with blocky chevrons, right angled prisms, heart shapes or dipyramidal shapes. A notch in the middle of a doubly terminated scalenohedron is a sure sign of a twinned crystal. lamellar twinning also seen resulting in striated cleavage surfaces. Pseudomorphs after many minerals are known, but easily identified as calcite. Also massive, fibrous, concretionary, stalactitic, nodular, oolitic, stellate, dendritic, granular, layered, etc. etc.
  • Cleavage is perfect in three directions, forming rhombohedrons.
  • Fracture is conchoidal.
  • Hardness is 3 (only on the basal pinacoidal faces, calcite has a hardness of less than 2.5 and can be scratched by a fingernail).
  • Specific Gravity is approximately 2.7 (average)
  • Streak is white.
  • Other Characteristics: refractive indices of 1.49 and 1.66 causing a significant double refraction effect (when a clear crystal is placed on a single line, two lines can then be observed), effervesces easily with dilute acids and may be fluorescent, phosphorescent, thermoluminescence and triboluminescent.
  • Associated Minerals are numerous but include these classic associations: Fluorite, quartz, barite, sphalerite, galena, celestite, sulfur, gold, copper, emerald, apatite, biotite, zeolites, several metal sulfides, other carbonates and borates and many other minerals.
  • Notable Occurrences include Pugh Quarry, Ohio; Rosiclare, Illinois; Franklin, New Jersey; Elmwood, Tennessee; Brush Creek and other Missouri, Wisconsin, Kansas and Oklahoma localities, USA; Andreasburg, Harz Mountains and Saxony, Germany; Brazil; Guanajuato, Mexico; Cornwall, Durham and Lancashire, England; Bombay area of India; Eskifjord, Iceland; many African localities as well as others around the world with their own unique varieties.
  • Best Field Indicators are crystal habit, reaction to acid, abundance, hardness, double refraction and especially cleavage.
 

THE MINERAL CALEDONITE

 

  • Chemistry: Cu2Pb5CO3(SO 4)3(OH)6, Copper Lead Carbonate Sulfate Hydroxide.
  • Class: Sulfates
  • Uses: As a very minor ore of lead and copper and as mineral specimens.
  • Specimens

Caledonite is seemingly a difficult mineral to classify in that it has both carbonate anions and sulfate anions. There are however more sulfates than carbonates in its formula and it would therefore seem to make the most sense to place it in the Sulfate Class as opposed to the Carbonate Class. The sulfate ion is also more complex and a stronger electronegative anion than the carbonate anion and mineralogists sometimes classify minerals in terms of their highest complexity and/or electronegativity. It is the same reasoning for not placing this mineral in the Oxide and Hydroxide Class in deference to its hydroxides. Other sulfates that contain carbonate anions in their formula include rapidcreekite, burkeite, hauckite, hanksite, nakauriite, tatarskite, mountkeithite, jouravskite and thaumasite (which has a silicon in its formula as well). There are several minerals, namely macphersonite, tychite, susannite, schrockingerite, leadhillite, nasledovite, motukoreaite, mineevite and brianyoungite; that contain more carbonates than sulfates and these are generally classified as carbonates; just to confuse the issue.
Caledonite is named for its country of original discovery . . . or at least that country's poetic name. The country is Scotland. Which is known in literature, especially poetry, as Caledonia, hence caledonite's name. Caledonite was first discovered at Leadhills, Lanarkshire, Scotland; a source of many interesting and unusual minerals. Caledonite is definitely one of those.

Caledonite forms small, but well formed and intricate crystals. It has a nice high luster, due to its lead content and a beautiful blue to green color due to its copper content. Caledonite is closely related to and often in association with linarite; CuPbSO4(OH)2. Linarite is normally a deeper blue and tabular or prismatic, but with a slanted, non-symmetrical termination. Caledonite and linarite are found in the oxidation zone of copper and lead ore deposits. Both minerals are beautiful and make for outstanding micromountable specimens.

 

PHYSICAL CHARACTERISTICS:

  • Color is green, light blue, blue to blue-green.
  • Luster is vitreous to resinous or greasy.
  • Transparency: Specimens are transparent to translucent.
  • Crystal System is orthorhombic; 2/m 2/m 2/m.
  • Crystal Habits include small micromountable prismatic and less often, tabular crystals with a truncation formed by multiple parallel domal and pyramidal faces. Acicular interlocking and radial aggregates are typical. Individual crystals can display a wide range of crystal faces.
  • Cleavage is perfect in one direction (basal) and poor in two (prismatic).
  • Fracture is uneven.
  • Hardness is 2.5 - 3.
  • Specific Gravity is approximately 5.6 - 5.8 (very heavy for translucent minerals).
  • Streak is greenish white to bluish-green.
  • Other Characteristics: Crystals usually striated.
  • Associated Minerals include leadhillite, cerussite, malachite, linarite, brochantite and anglesite.
  • Notable Occurrences include the type locality of Leadhills, Lanarkshire, Scotland as well as the fine specimens from the Mammoth-St Anthony Mine, Tiger, Arizona. Other locations include the Defense and Modoc mines and Cerro Gordo Mine, Inyo County and the Blue Bell Mine, San Bernardino, California; Beaver Creek, Utah and Dona Ana County, New Mexico, USA; Cornwall, England; Sardinia, Italy and Chile.
  • Best Field Indicators are crystal habit, density, color, streak, luster and cleavage.


THE MINERAL CALOMEL

 

  • Chemistry: HgCl, Mercury Chloride
  • Class: Halides
  • Uses: As a minor ore of mercury and as mineral specimens.
  • Specimens

Calomel is a somewhat rare mineral and is never found in large quantities. It is most often a secondary mineral that forms from the alteration of cinnabar or other mercury minerals. It also is deposited from hot underground solutions. Its common habit is as coatings on other minerals. The luster is very high and attractive and some specimens show a nice fluorescent red under ultraviolet light.

 

PHYSICAL CHARACTERISTICS:

  • Color is white, gray or yellow.
  • Luster is adamantine.
  • Transparency: Crystals are translucent.
  • Crystal System is tetragonal; 4/m 2/m 2/m
  • Crystal Habits are small tabular to pyramidal or horn-like crystals usually seen as coatings or crusts on other minerals.
  • Cleavage is distinct in one direction.
  • Fracture is conchoidal.
  • Hardness is 1 - 2.
  • Specific Gravity is 6.4 - 6.5 (very heavy for translucent minerals)
  • Streak is white.
  • Other Characteristics: Fluorescent red and crystals darken upon exposure to light over time.
  • Associated Minerals include mercury, cinnabar, metacinnabar and other mercury minerals.
  • Notable Occurrences include Almaden, Spain; Idria, Serbia; Hunan Prov., China and New Idria, California, Oregon, Terlingua, Texas, and Arkansas, USA.
  • Best Field Indicators are density, associations, fluorescence, hardness and crystal habit.

 

 

THE MINERAL CARBOCERNAITE

 

  • Chemistry: (Ca, Na)(Sr, Ce, Ba)(CO3)2 , Calcium Sodium Strontium Cerium Barium Carbonate.
  • Class: Carbonates
  • Group: Rare earth carbonates.
  • Uses: Only as mineral specimens and as a possible source of cerium.
  • Specimens

Carbocernaite is a rare mineral with an unusual chemistry. It is named in fact for its unusual chemistry reflecting the carbonate (carbo), cerium (cer) and sodium (Na) in its composition. Cerium is just one of the several rare earth metals that are important to industry. A closely related mineral is called burbankite. Both minerals are considered to be important in the development of rare earth metal containing minerals in carbonatite rocks and are being studied for this reason. Some rare earth minerals have been found to make pseudomorphs of burbankite and carbocernaite. A testament perhaps of how they play a role in the rare earth minerals' development. Although both contain some rare earth metals, neither is common enough to be considered at present a viable source for these important metals. Carbocernaite originates to some degree in hydrothermal deposits and nepheline syenites, but more substantially in carbonatite rocks, an unusual igneous rock composed mostly of carbonate minerals.

 

PHYSICAL CHARACTERISTICS:

  • Color is pale yellow, white, rose, brown and colorless.
  • Luster is vitreous to greasy.
  • Transparency: crystals are transparent to translucent.
  • Crystal System is orthorhombic.
  • Crystal Habits include small subhedral grains.
  • Cleavage is poor in several directions, but not usually seen.
  • Hardness is 3.
  • Specific Gravity is 3.5 - 3.6 (above average)
  • Streak is white.
  • Associated Minerals are albite, burbankite, bastnasite, ancylite-(Ce), cordylite, calcite, ankerite, sphene, monazite, rhabdophane, cerite, donnayite, synchysite-(Ce), pyrophanite and parisite.
  • Notable Occurrences are limited to the Weishan deposit, near Jinan City, Shandong Province, China; Mont Saint-Hilaire, Quebec, Canada and the type locality - Vourijarvi, Kola Peninsula, Russia.
  • Best Field Indicators: crystal habit, color, luster and locality.

 

 

THE MINERAL CARLETONITE

 

  • Chemistry: KNa4Ca4(CO3)4Si8O18 (F, OH) - H2O, Hydrated Potassium Sodium Calcium Carbonate Silicate Fluoride Hydroxide.
  • Class: Silicates
  • Subclass: Phyllosilicates
  • Group: Apophyllite
  • Uses: Only as mineral specimens.
  • Specimens
  • Carletonite is a rare silicate mineral that is found in only one location. It comes from the classic mineral locality of Mont Saint-Hilaire, Quebec, Canada. Crystals show good tetragonal prismatic form and can have a bright sapphire blue color. The darker blue crystals can demonstrate excellent pleochroism. Pleochroism is a condition in which the color of the crystal will change depending on the angle at which it is viewed. Carletonite varies from blue to white. Other pleochroic minerals include elbaite, spodumene, zoisite and cordierite. Some crystals have been cut as gems, but these are mostly for collectors as carletonite has low hardness and good cleavage. The largest known cut gem of carletonite weighs almost one and a half carats.
Carletonite is structurally interesting as well as beautiful. Like any member of the Phyllosilicates Subclass, carletonite's structure is layered with alternating silicate sheets and the potassium, sodium and calcium layers. Unlike other phyllosilicates, carletonite's silicate sheets are composed of interconnected four and eight-member rings. The sheets can be thought of as being like chicken wire with alternating octagon and square shaped holes. Both octagons and squares have a four fold symmetry and this is what gives carletonite its tetragonal symmetry; 4/m 2/m 2/m. Only carletonite and other members of the Apophyllite Group have this unique interconnected four and eight-member ring structure.

 

PHYSICAL CHARACTERISTICS:

  • Color is blue, white, colorless or pink. Color zoning is common.
  • Luster is vitreous to dull.
  • Transparency: Crystals are translucent to less commonly transparent.
  • Crystal System is tetragonal; 4/m 2/m 2/m
  • Crystal Habits include prisms truncated with a pinacoid termination. The prisms are predominantly four sided but may display small secondary faces giving a slight octagonal cross-section. Phantoms are seen in some transparent crystals.
  • Cleavage is perfect in one direction (basal) and fair in four directions (pyramidal).
  • Fracture is conchoidal.
  • Hardness is 4.5 - 5.
  • Specific Gravity is approximately 2.45 (slightly lighter than most translucent minerals)
  • Streak is white.
  • Other Characteristics: Prism faces are striated lengthwise and dark blue crystals show strong pleochroism.
  • Associated Minerals include rasvumite, tugtupite, aegirine, natrophosphate, sidorenkite, and other rare minerals.
  • Notable Occurrences are limited to one location; the type locality of Mont Saint-Hilaire, Quebec, Canada.
  

THE MINERAL CARNALLITE

 

  • Chemistry: KMgCl3 - 6H2O, Hydrated Potassium Magnesium Chloride.
  • Class: Halides
  • Uses: As a source of potash and a minor ore of magnesium and as mineral specimens.
  • Specimens

Carnallite is named for Prussian mining engineer, Rudolph von Carnall. It forms in marine evaporite deposits where sea water has been concentrated and exposed to prolonged evaporation. Carnallite precipitates with other potassium and magnesium evaporate minerals such as sylvite, kainite, picromerite, polyhalite and kieserite. Massive beds of carnallite are found but crystals are rare. The crystals will unfortunately absorb water from humid air (a process called deliquescence). This process can be eased by storing specimens in sealed dry containers.

Carnallite is an important source of potash, an invaluable fertilizer. Sylvite is the more important source of potash, but carnallite makes a significant contribution. Carnallite's magnesium output is of much lesser importance world wide but is still Russia's most significant source. Potassium is actually a common element, but unfortunately it is bound up in insoluble silicate minerals such as potassium feldspars. In order for potassium to be useful as a fertilizer it needs to be in a soluble form and thus soluble potassium salts are the source of choice.

These minerals are not that easy to form because evaporite minerals such as carnallite and sylvite as it turns out are some of the last minerals to evaporate from sea water. Minerals such as calcite, dolomite, gypsum, anhydrite and halite crystallize first in roughly that order. The conditions that must exist in order to have potassium and magnesium salts form involve having sea water contained in a cut off, but not completely isolated basin similar to the Black Sea. However the Black Sea does not form carnallite because it is not located in a warm enough climate as intensive evaporation is needed (this is an evaporite mineral after all). The basin must also not allow the concentrated brine to leave the basin so as to continually increase its salinity. The brine will sink to the bottom of the basin and allow fresher water to enter the basin which brings more magnesium into the basin. This has the effect of prolonging the crystallization of the salts and increasing the salinity of the brine. If evaporation does not progress this way, then the minerals listed above may fill the basin before the potassium salts have a chance to crystallize.


This scenario for potassium and magnesium salt formation is not observable today because current day basins such as the Black Sea, Hudson Bay, Persian Gulf, Red Sea, Baltic Sea or Sea of Japan have either the wrong shape or the wrong climatic conditions. But this was not always the situation in the geologic past as numerous ancient potassium and magnesium salt deposits have been found. Specifically the Permian, Devonian and Carboniferous time periods were excellent times for such basins and they are responsible for most of the worlds evaporite deposits. Most notable potassium and magnesium salt deposits are found in Carlsbad, New Mexico; the Paradox Basin in Colorado and Utah; deposits in Strassfurt, Germany; the Perm Basin, Russia and the Williston Basin in Saskatchewan, Canada.
Carnallite is relatively easy to distinguish from other evaporate minerals. Its taste is bitter and it has no cleavage, unlike halite. Carnallite is extremely light with a specific gravity of only 1.6 and it also shows a violet flame result when it is put in a gas flame due to its potassium content, unlike kieserite and other non-potassium salts.

 

PHYSICAL CHARACTERISTICS:

  • Color is white, colorless or yellow; rarely blue. Hematite inclusions may color specimens reddish.
  • Luster is vitreous to greasy, resinous or dull.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is orthorhombic; 2/m 2/m 2/m.
  • Crystal Habits are typically granular and massive, sometimes fibrous. Individual crystals are rare, but when seen are pseudo-hexagonal and tabular.
  • Cleavage is absent.
  • Fracture is conchoidal.
  • Hardness is 2.5
  • Specific Gravity is approximately 1.6 (light even for translucent minerals).
  • Streak is white.
  • Other Characteristics: Bitter taste, deliquescent (meaning it can absorb water from the air), fluorescent and can color a flame violet (due to potassium).
  • Associated Minerals include halite, anhydrite, dolomite, gypsum, kainite, kieserite, polyhalite, sylvite and other more rare potassium evaporite minerals.
  • Notable Occurrences include Carlsbad, New Mexico; Western Texas; Colorado and Utah, USA; Strassfurt, Germany; Ural Mountains, Russia; Iran; China; Tunisia; Spain; Mali; Ukraine and Saskatchewan, Canada.
  • Best Field Indicators are environment of formation, lack of cleavage, associations, density, deliquescence, fracture and taste.

THE MINERAL CARNOTITE

 

  • Chemistry: K2(UO2)2(VO4)2- 1-3H2O , Hydrated Potassium Uranyl Vanadate.
  • Class: Phosphates
  • Group: Vanadium Oxysalt
  • Uses: An important ore of uranium and vanadium and as mineral specimens.
  • Specimens

Carnotite is a relatively uncommon mineral, yet common enough to be an important ore of uranium and vanadium. Uranium and vanadium are two extremely strategic metals. Carnotite is closely related to tyuyamunite, Ca(UO2)2(VO4)2- 5-8H2O. The chemistries are very similar with potassium replacing calcium and a different percentage of water, however the structures are slightly different as tyuyamunite is orthorhombic and carnotite is monoclinic. The two minerals are often found together and are essentially indistiguishable by ordinary methods. Meteoric oxygenated waters dissolve the uranium from primary uranium minerals and the uranium is later deposited in reducing enviroments more favorable to the formation of carnotite. Since many deposits in sandstones are associated with petrified trees and other fossils, it is reasonable to assume that the decaying material helped produce the required reducing enviroment. Carnotite is an uncommon and interesting uranium mineral that can coat host rocks with an attractive yellow powder. Remember, this is also a radioactive mineral and should be stored away from other minerals that are affected by radioactivity and human exposure should always be limited.

 

 

 

 

PHYSICAL CHARACTERISTICS:

  • Color is bright yellow.
  • Luster is pearly to dull or earthy.
  • Transparency: Crystals are translucent to opaque.
  • Crystal System is monoclinic; 2/m
  • Crystal Habits include crusts, earthy masses, foliated and granular aggregates.
  • Cleavage is perfect in one direction.
  • Fracture is uneven.
  • Hardness is 2.
  • Specific Gravity is approximately 4 - 5 (heavy for translucent minerals), higher gravity with lower water content.
  • Streak is yellow.
  • Associated Minerals include other uranium and vanadium minerals in sandstones and limestones.
  • Other Characteristics: Radioactive and not fluorescent.
  • Notable Occurrences include many locations in Wyoming, Colorado, Arizona, Utah, Grants, New Mexico and Mauch Chunk, Carbon Co, Pennsylvania, USA; Shaba, Zaire; Morocco; Radium Hill, Australia and Kazakhstan.
  • Best Field Indicators are bright yellow color, density, habit, lack of any fluorescence, radioactivity and associations.

 

THE MINERAL CASSITERITE

 


Cassiterite is a mineral that has ornately faceted specimens with high luster. It is generally opaque, but its luster and multiple crystal faces cause a nice sparkle. Cassiterite has been an important ore of tin for eons and is still the greatest source of tin today. Most sources of cassiterite today are not primary deposts but alluvial deposits containing weathered grains. The best source of original-formation cassiterite is at the tin mines of Bolivia, where it is found in hydrothermal veins. Although found throughout the world in many igneous rocks, cassiterite is usually only a minor constituent. The Bolivia veins and those worked and nearly exhausted in Cornwall, England, somehow concentrated the tin in a way not fully understood by geologists.

Twinning is common in cassiterite and most aggregate specimens show crystal twins. The typical twin is bent at a near-60-degree angle, forming an "Elbow Twin". Multiple twinning can continue to bend the crystal around and possibly form a cyclic twin. However, cassiterite does not form this type of twin as often as its mineral cousin, rutile.

 

PHYSICAL CHARACTERISTICS:

  • Color is black or reddish brown or yellow.
  • Luster is adamantine or greasy.
  • Transparency crystals are transparent in thin crystals otherwise opaque.
  • Crystal System is tetragonal; 4/m 2/m 2/m
  • Crystal Habits include eight-sided prisms and blocky or stubby crystals terminated by a blunt four-sided or complex pyramid. The prisms are composed of two four sided prisms with one of the prisms being dominant. Also thin acicular needles or blades are common. Can be massive, granular, fibrous and botryoidal. A concretionary form combined with quartz and hematite is called "wood-tin".
  • Cleavage is good in two directions forming prisms, poor in a third (basal).
  • Fracture is conchoidal to uneven.
  • Hardness is 6 - 7
  • Specific Gravity is 6.6 - 7.0+ (very heavy for non-metallic minerals)
  • Streak is white, but at times brownish.
  • Associated Minerals include, but are not limited to, tourmalines, molybdenite, bismuthinite, topaz, fluorite, arsenopyrite and wolframite.
  • Other Characteristics: high refractive index of approximately 2.0.
  • Notable Occurences include the La Paz and Colquiri areas of Bolivia; Cornwall, England; Durango, Mexico; Malaya; Indonesia; Russia and China.
  • Best Field Indicators are crystal habit, hardness, twinning and high index of refraction (luster).

 

THE MINERAL CATAPLEIITE

 


Catapleiite is a rather rare zirconium mineral. It forms in alkaline rocks and rare rocks known as agpaites which are igneous rocks of unusual concentrations. They are characterized by high concentrations of alkali metals especially sodium and low concentrations of silicon and aluminum. They are feldspar and feldspathoid rich and being low in silicon, contain little or no quartz. Agpaite pegmatites contain unusual minerals because they originate with unusual elements. Elements such as beryllium, zirconium, titanium, niobium, barium, strontium, thorium and rare earth metals are all found in the compositional mix that represents this rock type.

There exists agpaite in several places around the world, but by far the most famous are the ones at the Kola Peninsula in Russia, Narsarsuk, Greenland and the one above all the rest, the mines of Mount Saint Hilaire, Quebec, Canada. Catapleiite is just one of the rare minerals that can form in these silica starved, unique chemical environments. Other minerals coming from these unique localities include leifite, synchysite, serandite, elpidite, aegirine, arfvedsonite, eudialyte and analcime to name a few.

Catapleiite is dimorphous with the mineral gaidonnayite. Dimorphous means that both minerals have the same chemistry, but they have different structures. Catapleiite is monoclinic (pseudohexagonal) while gaidonnayite is orthorhombic. Catapleiite is also in a series with the mineral calcium catapleiite in which the sodium of catapleiite is replaced with a calcium ion instead. In a series, the structure remains the same, but the chemistry is different.
Catapleiite although quite rare, forms at several localities around the world. But it is the magnificent specimens of rosette clusters found only at Mount Saint Hilaire that demonstrate the mineral's true beauty. Its rarity, beauty, unusual chemistry, classic locality and cool name make catapleiite a great addition to a mineral collection.

 

PHYSICAL CHARACTERISTICS:

  • Color is blue, gray, pale yellow, yellowish-brown, reddish or colorless.
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is monoclinic; 2/m.
  • Crystal Habits include pseudohexagonal plates or lamellar masses. Splendid rosettes are also known. Twinning is common.
  • Cleavage is perfect in one direction.
  • Hardness is 5 - 6.
  • Specific Gravity is 2.8
  • Streak is white.
  • Associated Minerals include feldspars, feldspathoids and Sphene among many rare species.
  • Notable Occurrences include Magnet Cove, Arkansas, USA; Madagascar; Laven, Langesundfjord, Norway and Mount Saint Hilaire, Quebec.
  • Best Field Indicators are crystal habit, locality and color.

 

 THE MINERAL CAVANSITE

 


Cavansite is a beautiful and rare mineral. It was only discovered in the last 30 years and is found in only a few locallities. By far the best crystals come from the famous zeolite quarries in Poona, India. Crystal aggregates consist of spherical rosettes with jutting pointed crystals. The deep blue color of even the smallest cavansite crystals is truly amazing. A beautiful blue cavansite rosette perched on top of the muted colors of the typical zeolites makes a dramatic crystal association. Cavansite's rarity and beauty explain its recent popularity.

 

PHYSICAL CHARACTERISTICS:

  • Color is greenish-blue to ocean blue.
  • Luster vitreous to pearly.
  • Transparency transparent to translucent.
  • Crystal System: Orthorhombic
  • Crystal Habits radiating acicular crystals forming spherical crystal clusters.
  • Cleavage perfect in one direction.
  • Fracture conchoidal.
  • Hardness 3 - 4
  • Specific Gravity is approximately 2.33
  • Streak is blue.
  • Associated Minerals include zeolites such as stilbite and heulandite as well as calcite, apophyllite , babingtoniteand quartz.
  • Other Characteristics: larger crystals show an unusual internal reflection.
  • Notable Occurrence is Poona, India and Columbia Co. and Malheur Co., Oregon, USA.
  • Best Field Indicators are color, associations, locality and crystal habit.

 

 

THE MINERAL CELESTITE

 


Celestite is a favorite among mineral collectors. Its sky blue (or celestial) color is very pretty, and is unique in the mineral kingdom. Celestite also forms with other colorful minerals, making very nice combinations. Blue Celestite with bright yellow sulfur is one of the most famous colorful combinations of minerals. Celestite has the same structure as Barite (BaSO4), and forms very similar crystals. The two may seem identical by ordinary methods, but a flame test can distinguish them. By scraping the dust of the crystals into a gas flame, the color of the flame will confirm the identity of the crystal. If the flame is a pale green, it is barite, but if the flame is red, it is celestite. The flame test works because the elements barium (Ba) and strontium (Sr) react with the flame and produce those colors. Normally barite is not blue, but many specimens of blue barite are often misidentified as celestite. The nice crystals, good luster and attractive blue color make fine specimens of celestite an outstanding mineral for someone's cabinet or display case.

PHYSICAL CHARACTERISTICS:

  • Color is usually blue but can also be colorless, yellow and tints of red, green and brown.
  • Luster is vitreous.
  • Transparency crystals are transparent to translucent.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include the bladed crystals that are dominated by two large pinacoid faces top and bottom and small prism faces forming a jutting angle on every side. There are many variations of these faces but the flattened blades and tabular crystals are the most common. If the pinacoid faces become diminished or are absent, the resulting prismatic crystal has a rhombic cross section. This habit is rather common in specimens from Madagascar. Also nodular, fibrous or granular.
  • Cleavage is perfect in one direction, less so in another direction.
  • Fracture is conchoidal.
  • Hardness is 3 - 3.5
  • Specific Gravity is approximately 3.9+ (above average for translucent minerals)
  • Streak is white.
  • Associated Minerals are calcite, gypsum, strontianite, sulfur and fluorite.
  • Other Characteristics: red color in flame test (see above), some specimens fluoresce under UV light.
  • Notable Occurances include Lake Erie region of Ohio, Michigan and New York USA; Madagascar; Sicily and Germany.
  • Best Field Indicators are crystal habit, color and flame test.

THE MINERAL CERUSSITE


Cerussite is a popular collection mineral. It is famous for its great sparkle, great density and amazing twinned crystals. Cerussite is a minor ore of lead. It has a very high luster due mostly to the lead content. Just as leaded crystal glass sparkles more brilliantly because of its lead content, so too does cerussite. The lead raises the index or refraction of cerussite to just over 2.07. The lead is also responsible for its increased specific gravity. Cerussite has one of the highest densities for a transparent mineral. It is over six and a half times as dense as water. Most rocks and minerals average only around three times the density of water.

Crystallographers can appreciate cerussite's sparkle and density; but it is cerussite's wonderfully twinned crystals that get them excited! This mineral can form some geometrically intricate structures and spoked star shapes that simply are amazing. Cerussite belongs to the Aragonite Group of minerals. A group that as a whole is well known for twinning with commonly twinned members such as aragonite, witherite and strontianite Twinning is most definitely common in cerussite and besides the intricate structures mentioned already, singular twins are also interesting. There are three basic types of twinning in cerussite: Elbow or chevron shaped twins, cyclic twins and last but not least, reticulated twins. The elbow or chevron shaped twins are the most common and are generally seen on most specimens. The cryslic twins often form star shapes with six "spokes" extending from the star. Very beautiful! The reticulated twins are classics and form complex interconnected beams of crystals. So intricate are these specimens they appear to have been constructed. They truly are an awesome mineralogical wonder. Cerussite twins are a must for collectors who are fond of twinned crystals.


Cerussite is found in the oxidation zone of lead deposits usually associated with galena. Some specimens show cerussite crusts around a galena core as the oxidation was "caught in the act" so to speak. Cerussite can make nice associations with galena and another lead mineral anglesite, a yellow colored, lead sulfate. Cerussite is simply a classic!  

The name "cerussite" is from the Latin word cerussa, meaning white lead.  It is also commonly misspelled, often with only one "s", or with two r's, or both: cerrussite, cerusite, and cerrusite are all seen instead of the correct spelling, cerussite.  It has also been known as Horn Silver and lead spar.

 

PHYSICAL CHARACTERISTICS:

  • Color is usually colorless or white, also gray, yellow, and even blue-green.
  • Luster is adamantine to almost submetallic and sometimes greasy.
  • Transparency Crystals are transparent to translucent.
  • Crystal System is orthorhombic; 2/m 2/m 2/m.
  • Crystal Habits twinning is common and expected (see above), single crystals can be prismatic with blunted pyramidal terminations. Some specimens show acicular white crystals. Also, reniform, earthy, and crusty varieties are found.
  • Cleavage is not as good as other carbonates, but still considered good in one direction.
  • Fracture is conchoidal and brittle.
  • Hardness is 3-3.5.
  • Specific Gravity is 6.5+ (very dense for a generally transparent mineral).
  • Streak is white or colorless.
  • Other Characteristics: Refractive index of 2.07 (very high) and prismatic crystals are striated lengthwise.
  • Associated Minerals are barite, calcite, anglesite, and other secondary minerals and especially galena.
  • Notable Occurrences include Tsumeb, Nambia; Congo; Morocco; Australia; Germany and Arizona, USA.
  • Best Field Indicators are its crystal habit (especially twins), heaviness, high refraction and luster.

 

THE MINERAL CHALCANTHITE

 

  • Chemistry: CuSO4 - 5H2O, Hydrated Copper Sulfate.
  • Class: Sulfates
  • Group: Chalcanthite
  • Uses: A minor ore of copper, various chemical uses and as mineral specimens.
  • Specimens

Chalcanthite is one of only a few water soluble sulfate minerals. This fact drives much of what is interesting about this mineral. It forms in the near-surface secondary oxidation zone of copper deposits usually late in the development of these deposits. Since it is so soluble, it may crystallize, dissolve and recrystallize again and again before the deposit is discovered.

In wetter regions, chalcanthite is not found in large amounts (originally), but in arid regions, such as in Chile, chalcanthite is a major ore. Any sulfate rich ground water that might leach out copper from other copper minerals, will crystallize chalcanthite when the water has a chance to evaporate. In many copper mines, chalcanthite is an ongoing precipitate forming blue encrustations, crystal aggregates and stalactites right on the sides of the mine's shafts.
It is this ease of crystallization that is the bane of natural chalcanthite crystals, at least with respect to mineral collectors. More often than not, excellent crystals for sale from mineral dealers are fakes or more specifically, artificially grown crystals from a solution of copper sulfate in someone's house or shop. If they are natural, they often have such a wonderful color, striking form and beautiful clarity, that they are then deemed too perfect to be real and thus regarded as fakes when they actually are not. What's a dealer to do?

In any respect, chalcanthite's solubility is its other enemy. Many fine specimens in museums and in private collections have met their doom as they slowly absorb water from the air and then lose it again. Over time, this cycle leads to the destruction of what once might have been a world class specimen into a pile of bluish dust. Curators and concerned collectors store their specimens in sealed containers with desiccants to postpone these destructive effects. Some chalcanthite seems resistant to water absorption and this resistance seems tied to the purity of the specimen, especially the lack of iron impurities.

Chalcanthite does have useful purposes or at least solutions of copper sulfate do. It is a wonderful tool to use to teach children how some crystals form. In a class room or at home with adult supervision, chalcanthite crystals can form easily over a few days time from a warm solution of copper sulfate left to evaporate. The always attractive blue color and the sparkling crystals help to keep the children interested. Adult supervision is strongly suggested as chalcanthite and copper sulfate solutions are poisonous.

There are many chemical uses for copper sulfate solutions. Copper sulfate solutions and crystals are a staple in well stocked chemistry labs. Metallic copper can be obtained from copper sulfate solutions by adding metallic iron. A process used in the mining and processing of chalcanthite. As a poison, copper sulfate solutions or crystals were used to clear ponds and waterways of plant growth, but this practice has stopped due to the greater environmental concerns.
Identification of the mineral chalcanthite is generally pretty easy. Its bright blue color can be dulled on natural specimens, but it is otherwise very distinctive. Its solubility is also key if this test can be done with a small unnecessary fragment of the specimen in question. The resulting solution should turn blue. Another relatively common soluble sulfate is melanterite, FeSO4 - 7H2O, but it is generally greener.

Taste is a test that is used for some minerals such as halite and can be used on chalcanthite. Chalcanthite has a sweet metallic taste that is distinctive. However, it is not recommended as a test to be done casually for as was stated, chalcanthite is poisonous! If it is necessary, use a tip-of-the-tongue technique to minimize the risk.
Chalcanthite loosely translated from the Greek means copper flower. An apt name for this attractive mineral. Synonyms include "blue stone" and "copper vitriol". Chalcanthite is the name of a group of only four triclinic sulfates of which chalcanthite is its only common member. Other members have in place of copper ions of iron, manganese and magnesium.

These are the members of the Chalcanthite Group:
  • Chalcanthite (Hydrated Copper Sulfate)
  • Jokokuite (Hydrated Manganese Sulfate)
  • Pentahydrite (Hydrated Magnesium Sulfate)
  • Siderotil (Hydrated Iron Sulfate)

Specimens of chalcanthite are one-of-a-kind and are generally affordable. Natural specimens from an honest dealer are preferred, but are hard to get. Fakes, when sold as such, have their brilliant color and attractiveness to at least deserve consideration for placement in someone's collection.

 

PHYSICAL CHARACTERISTICS:

  • Color is a bright and deep blue.
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is triclinic; bar 1.
  • Crystal Habits include rare, individual, natural crystals showing well formed slanted prismatic, tabular or lense-shaped forms, more commonly aggregated into columnar, curved, parallel growth structures. Also found as encrusting, stalactitic and granular masses and as vein filling deposits.
  • Cleavage is poor (basal).
  • Fracture is conchoidal.
  • Hardness is 2.5
  • Specific Gravity is approximately 2.2 - 2.3 (noticeably below average).
  • Streak is pale blue to colorless.
  • Other Characteristics: Is very soluble in water. A fact that is a detriment to most collection specimens as they may absorb water from the air and deteriorate over time. The taste has a sweet metallic character, but do not do this test often or with more than just a tip-of-the-tongue technique and only if needed to confirm an identification as chalcanthite is poisonous!
  • Associated Minerals are brochantite, calcite , melanterite, aragonite, malachite and chalcopyrite.
  • Notable Occurrences include Chuquicamata and El Teniente (Sewell), Chile; Minas de Rio Tinto, Spain; England; Germany and Ireland and in the United States, Bigham Canyon, Utah; Ducktown, Tennessee; Imlay, Pershing County, Nevada; Arkansas; California; New Mexico and Arizona.
  • Best Field Indicators are crystal habit, low density, associations, solubility in water, taste and color.

 

 

THE MINERAL CHALCOCITE

 

  • Chemistry: Cu2S, Copper Sulfide
  • Class: Sulfides
  • Uses: As a minor ore of copper and as mineral specimens.
  • Specimens

Chalcocite is an important copper mineral ore. It has been mined for centuries and is one of the most profitable copper ores. The reasons for this is its high copper content (67% atomic ratio and nearly 80% by weight) and the ease at which copper can be separated from sulfur. It is not however the primary ore of copper due to its scarcity. Although the richest chalcocite deposits have probably been mined out, it is still being mined and will almost certainly always be mined in the future.

Chalcocite occurs as a secondary mineral in many ore bodies in a zone called the supergene enrichment zone. Called a secondary enrichment mineral, although also a primary mineral as well, chalcocite commonly forms from the alteration of primary copper minerals that are attacked above the water table by oxygen. The oxygenated copper fluids descend to the water table where a reaction with primary ores results in the copper being reduced back to a sulfide, most commonly chalcocite. Ore bodies will have a layer of chalcocite which corresponds to the present or a past water table level and this layer is called a "chalcocite blanket". The chalcocite blanket is richer in copper than the upper oxidized portion of the ore body and usually richer than the primary unaltered ores below. The chalcocite blanket represents a real gold mine, or should that be copper mine, to the copper prospectors.

Fine crystals of chalcocite are quite uncommon and are much sought after. The now depleted mines at Cornwall, England and Bristol, Connecticut produced the most famous clusters of wonderfully formed chalcocite crystals. Some new localities with well formed crystals are promising, but so far the specimens from those old mines are the only good chalcocite crystals available on the market. The heavily striated pseudohexagonal tabular crystals are real classics for the mineral collector and often command an equally classic price.

Since chalcocite is a secondary mineral that forms from the alteration of other minerals, it has been known to form pseudomorphs of many different minerals. A pseudomorph is a mineral that has replaced another mineral atom by atom, but it leaves the original mineral's crystal shape intact. Chalcocite has been known to form pseudomorphs of the minerals bornite, covellite, chalcopyrite, pyrite, enargite, millerite, galena and sphalerite. Pseudo means false and morph means shape or form, thus pseudomorph means false shape since the mineral is chalcocite but the shape is that of a covellite crystal, for example.

 

PHYSICAL CHARACTERISTICS:

  • Color is dark gray to black.
  • Luster is metallic.
  • Transparency: Crystals are opaque.
  • Crystal System is orthorhombic; 2/m 2/m 2/m below 105 degrees celsius and hexagonal; 6/m 2/m 2/m above 105 degrees celsius.
  • Crystal Habits include pseudohexagonal tabular to prismatic crystals often with a shallow pyramidal truncation with a flat point. Also found massive and compact. Twinning is common and sometimes results in a six pointed star shaped cyclic twin called a trilling or in elbow shaped twins.
  • Cleavage is imperfect in two directions, prismatically.
  • Fracture is conchoidal.
  • Hardness is 2.5 - 3
  • Specific Gravity is approximately 5.5 - 5.8 (above average for metallic minerals)
  • Streak is shiny black to lead gray.
  • Other Characteristics: Crystals are usually deeply grooved with lateral striations and a tarnish will tend to dull the luster of crystals over time.
  • Associated Minerals are quartz, enargite, malachite, azurite, copper, cuprite, tetrahedrite, bornite, tennantite, chalcopyrite, covellite, pyrite and other sulfides.
  • Notable Occurrences include Bristol, Connecticut, Butte, Montana, Morenci and Bisbee, Arizona and Bingham Canyon, Utah, Ducktown, Tennessee, USA; Cornwall, England; Tsumeb, Namibia; Tuscany, Italy and Rio Tinto, Spain.
  • Best Field Indicators are crystal habit, streak, striations, color and associations.

 

THE MINERAL CHALCOPHYLLITE

 

  • Chemistry: Cu18Al2 (AsO4)3(SO4)3(OH)27 - 33H2O , Hydrated Copper Aluminum Arsenate Sulfate Hydroxide
  • Class: Phosphates
  • Subclass: Arsenates
  • Uses: a very minor ore of copper and as mineral specimens.
  • Specimens

Chalcophyllite, which is named from the Greek words for copper and leaf, is a rare secondary mineral that forms in the oxidation zone of copper ore deposits. It is a great collection mineral because it has a high luster, an attractive blue-green to green color and it forms nice tabular six-sided crystals that can be arranged into rosettes. Its crystals are similar to those of spangolite. Chalcophyllite has a green streak and that combined with its crystal habit make chalcophyllite difficult to misidentify.

Chalcophyllite is yet another in the long list of rare and classic Cornwall minerals. It is associated there with other rare copper minerals such as cornubite, tyrolite, caledonite, devilline and connellite. Other colorful but less rare associated minerals include malachite and chrysocolla.

Chalcophyllite is unusual in that it has three different anion groups in its chemistry. Most minerals have just one principle anion group with possibly some hydroxides or halides along for the ride. Classifying those minerals is relatively easy as they are generally classed by their most complex or highest electronegative anion group. In the case of chalcophyllite, it has the same number of arsenate anion groups as sulfate anion groups. Should it be classified in the Sulfate Class or as an arsenate? Mineralogists prefer to classify it as a phosphate (where arsenates are placed) because the arsenate group has a higher negative charge (-3) than the sulfate group (-2).

Another unusual aspect of chalcophyllite's chemistry is its large amount of hydroxides and water molecules. Half of this mineral is either water or hydroxide! Generally copper minerals have a higher than average density, but with a specific gravity of 2.4 - 2.7, chalcophyllite is actually below average.

 

PHYSICAL CHARACTERISTICS:

  • Color is blue-green to emerald green.
  • Luster is adamantine, vitreous to pearly.
  • Transparency crystals are transparent to translucent.
  • Crystal System is trigonal; bar 3.
  • Crystal Habits include tabular to platy crystals and lamellar masses. Some specimens have been partially pseudomorphed by chrysocolla and appear much duller in luster.
  • Cleavage: is perfect in one direction (basal).
  • Fracture: Uneven.
  • Hardness is 2
  • Specific Gravity is approximately 2.4 - 2.7 (light for copper minerals).
  • Streak is green.
  • Associated Minerals include cornubite, tyrolite, cuprite, caledonite, malachite, chalcopyrite, chrysocolla, devilline and connellite.
  • Notable Occurrences are limited to Chile; France; Germany; Wheal Gorland, Wheal Unity and other mines in Cornwall, England and Arizona, Utah and Nevada, USA.
  • Best Field Indicators are crystal habit, streak, locality, associations, density and color.

 

 

THE MINERAL CHALCOPYRITE

 

  • Chemistry: CuFeS2, Copper Iron Sulfide
  • Class: Sulfides
  • Group: Chalcopyrite
  • Uses: Major ore of copper
  • Specimens

Chalcopyrite (or copper pyrite), looks like, and is easily confused with Pyrite, FeS2. Chalcopyrite is one of the minerals refered to as "Fool's Gold" because of its bright golden color. But real gold is a more buttery yellow and is ductile and malleable.

As an ore od copper, the yield of chalcopyrite is rather low in terms of atoms per molecule. It is only 25%, compared to other copper minerals such as chalcocite, Cu2S - 67%; cuprite, Cu2O - 67%; covellite, CuS - 50% or bornite Cu5FeS4 - 50%. However the large quantities and widespread distribution of chalcopyrite make it the leading source of copper. Chalcopyrite is a common mineral and is found in almost all sulfide deposits. Fine crystals of chalcopyrite have a unique character and can add to anyone's collection.

 

PHYSICAL CHARACTERISTICS:

  • Color is brassy yellow, tarnishes to irredescent blues, greens, yellows and purples.
  • Luster is metallic.
  • Transparency: Crystals are opaque.
  • Crystal System is tetragonal; bar 4 2m
  • Crystal Habits are predominantly the disphenoid which is like two opposing wedges and resembles a tetrahedron. Crystals sometines twinned. Also commonly massive, and sometimes botryoidal.
  • Cleavage is rather poor in one direction.
  • Fracture is conchoidal and brittle.
  • Hardness is 3.5-4
  • Specific Gravity is approximately 4.2 (average for metallic minerals)
  • Streak is dark green.
  • Other Characteristics: Some striations on most crystal faces.
  • Associated Minerals are quartz, fluorite, barite, dolomite, calcite, pentlandite, pyrite and other sulfides.
  • Notable Occurances include Chile, Peru, Mexico, Europe, South Africa, several USA sites and many others around the world.
  • Best Field Indicators are crystal habit, tarnish, softness and brittleness.

 

THE MINERAL CUPRITE

 


Cuprite has been a major ore of copper and is still mined in many places around the world. Of all the copper ores except for native copper, cuprite gives the greatest yield of copper per molecule since there is only one oxygen atom to every two copper atoms. As a mineral specimen, cuprite shows fine examples of well-developed cubic crystal forms. Cuprite's dark crystals show internal reflections of the true deep red inside the almost black crystal. Other varieties, such as chalcotrichite, show tufts of needle-like crystals that have a beautiful red color and a special sparkle that make them popular display cabinet specimens.

PHYSICAL CHARACTERISTICS:

  • Color is red to a deep red that can appear almost black.
  • Luster is adamantine or submetallic to dull or earthy if massive.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is isometric; once thought to be 4 3 2 but now believed to belong to 4/m bar 3 2/m.
  • Crystal Habits include the cube, octahedron, dodecahedron, and combinations of these forms. Some display faces of the obscure gyroid form. A variety known as Chalcotrichite forms long needle-like crystals or fuzzy crusts. also massive.
  • Cleavage is fair in four directions forming octahedrons.
  • Fracture is conchoidal.
  • Hardness is 3.5-4
  • Specific Gravity is approximately 6.0 (very heavy for translucent minerals)
  • Streak is brick red.
  • Associated Minerals are limonite, copper, chrysocolla, malachite and other secondary copper minerals.
  • Other Characteristics: Forms a surface film with long exposure to strong light. Crystals of cuprite are sometimes altered or partially altered to malachite and rarely copper.
  • Notable Occurrences include Arizona, USA; Africa; Australia; Chile and several localities in Europe.
  • Best Field Indicators are color, crystal form and softness.

 

THE MINERAL CHAROITE

 

  • Chemistry: K(Na, Ca)11(Ba, Sr)Si18O46(OH, F)-nH2O, Hydrated Potassium Sodium Calcium Barium Strontium Silicate Hydroxide Fluoride.
  • Class: Silicates
  • Subclass: Inosilicates
  • Uses: an ornamental stone and also as gemstones.
  • Specimens

Charoite is an unsual mineral and of rare occurence. It is found to date in only one location: along the Chary River at Aldan in Russia. It formed from alteration of limestones by the close presences of an alkali-rich nephline syenite intrusion. The heat, pressure and more importantly, the infusion of unique chemicals into the rock is responsible for the transformations into new minerals such as charoite. Why charoite has not been found in other locations is not fully understood. But it is probably due to a combination of a chemically unique limestone reacting with a chemically unique intrusion and subjected to unique physical conditions.

Charoite is used as an ornamental stone and as a gemstone. It forms a swirling pattern of interlocking crystals. The color of charoite is described as a stunning lavender, lilac, violet and/or purple. All can be used as all are probably present in every swirling example. The look of charoite is unlike any other mineral and can't be mistaken. It has the appearance of purple marble, but really defies description. Its popularity would probably be much greater if not for its "synthetic" character. It simply looks unnaturally beautiful.

 

PHYSICAL CHARACTERISTICS:

  • Color is white, lavender, lilac, violet and/or purple.
  • Luster vitreous to pearly.
  • Transparency transparent to translucent.
  • Crystal System: monoclinic
  • Crystal Habit is of fibrous interlocking crystal masses.
  • Cleavage is not observed since it is exclusively massive.
  • Fracture conchoidal.
  • Hardness 5
  • Specific Gravity is approximately 2.5 - 2.8 (average)
  • Streak is pale purple.
  • Notable Occurrence is solely the Chary River at Aldan in Russia.
  • Best Field Indicators are color, locality and habit.

 

THE MINERAL CHENGDEITE

 


Chengdeite is one of the most dense minerals known. At a specific gravity of 19.3 it far exceeds all but a very few minerals. Gold is about 9% lighter at a lowly SG of 17.65 and platinum is slightly better at 18.00. Chengdeite in fact is only beat out by minerals that are more enriched in iridium and/or osmium; specifically the minerals iridium, osmium and iridosmine, an iridium/osmium alloy. Iridium, at a calculated density of 22.65 grams per cubic centimeter, is probably the densest element known to man. Although osmium, at 22.61 g/cubic cm, is close enough to make the distinction difficult. Most people think lead is the most dense! But at 11.37 g/cm3, its barely halfway there!

Chengdeite is classified as an element dispite the fact, that in chemical reality, it is a compound! Minerals like chengdeite are alloys with metallic bonds that are very similar to the more pure metallic elements and are thus classified as elements. Chengdeite is very rare and new to the mineral world. It is named for Chengde County, China from where it was discovered in placer deposits in just the early 1990's. Since then it has been found as a trace mineral in chromite rich ultra-mafic igneous deposits.

 

PHYSICAL CHARACTERISTICS:

  • Color is black.
  • Luster is metallic.
  • Transparency: Specimens are opaque.
  • Crystal System is isometric; bar 4 3 m.
  • Crystal Habits include nuggets found in placer deposits.
  • Cleavage is absent.
  • Fracture is hackly.
  • Hardness is 5
  • Specific Gravity is 19.3 (well above average, even for a metallic mineral)
  • Streak is black.
  • Associated Minerals include olivine, chromite and other ultra-mafic igneous minerals.
  • Notable Occurrences are limited to the type locality at Luan River in Chengde County, China and just a few ultra-mafic igneous rock deposits.
  • Best Field Indicator is crystal habit, color, locality and especially density.

 

THE MINERAL CHILDRENITE

 

  • Chemistry: (Fe, Mn)AlPO4(OH)2 - H2O, Hydrated Iron Manganese Aluminum Phosphate Hydroxide.
  • Class: Phosphates
  • Uses: Only as mineral specimens.
  • Specimens

Childrenite is a classic secondary mineral that was first discovered in the mines of Devon, England especially the classic George and Charlotte Mine near Tavistock. It most likely forms from the alteration of primary granitic phosphates such as lithiophilite and triphylite when aluminum and water are available. Childrenite is also found in some ore veins.

Childrenite forms a solid solution series with the mineral eosphorite. Eosphorite's formula is (Mn, Fe)AlPO4(OH)2 - H2O and differs from childrenite only by being rich in manganese instead of iron. The structures of the two minerals are the same and therefore it would be expected that their differences in physical properties between the two would be related to the iron/manganese percentage. Eosphorite is less dense and is generally pinkish to rose-red in color whereas childrenite's colors tends towards various shades of brown. In terms of crystal habits the two also differ. Eosphorite forms prismatic, slender crystals and rosettes. Childrenite forms tabular or bladed individuals or lamellar aggregates. It has been said that the two different habits belie their solid solution relationship.

 

 

 

 

 

PHYSICAL CHARACTERISTICS:

  • Colors include dark yellow, yellow-brown and brown.
  • Luster is vitreous.
  • Transparency: Specimens are transparent to translucent.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include equidimensional tabular, bladed or platy crystals. Aggregates include lamellar, parallel growth and fibrous habits.
  • Cleavage is good in two directions at right angles.
  • Fracture is conchoidal.
  • Hardness is 4.5 - 5.
  • Specific Gravity is approximately 3.2 (slightly above average).
  • Streak is white.
  • Associated Minerals include quartz, feldspars, lithiophilite, chlorite, pyrite, hureaulite and triphylite.
  • Notable Occurrences include the classic George and Charlotte Mine near Tavistock, Devon and some mines in Cornwall, England; Custer, South Dakota, USA and Minas Gerais, Brazil.
  • Best Field Indicators are crystal habit, color, associations, localities and density.

 

THE MINERAL CHKALOVITE

 


Chkalovite is a rare beryllium silicate mineral. Other more common and more famous beryllium silicates are beryl, phenakite, euclase and bertrandite. Chkalovite is far too rare to be considered an ore of beryllium.
Chkalovite is found in agpaitic pegmatites, a type of igneous rock that is rich in sodium and poor in silicon and aluminum compared to other typical igneous rocks. Many new and exotic minerals are discovered wherever this rock type is found. The agpaitic pegmatites of the Kola Peninsula, Russia; Langesundfjord, Norway; Ilimaussaq, Greenland and especially Mont Saint-Hilaire, Quebec, Canada are the most famous of these rock types and for good reason. They have produced hundreds of new mineral species such as chkalovite. Chkalovite's type locality (the place it was first discovered) is the eastern slope of Malyi Punkaruaiv Mountain in the Lovozero Massif of the Kola Peninsula. It was discovered there in 1936.

Chkalovite is typically colorless or white and crystals are complex and not always so well formed. As a result, it is often hard to find and recognize. Despite these difficulties some specimens are finding their way onto the mineral markets. Often associated with other rare minerals, chkalovite can make an interesting specimen.

 

PHYSICAL CHARACTERISTICS:

  • Color is colorless and white.
  • Luster is vitreous to greasy.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is orthorhombic; m m 2.
  • Crystal Habits include mostly equant (often complex) to prismatic forms.
  • Cleavage indistinct in one direction.
  • Fracture is uneven to conchoidal.
  • Hardness is 6.
  • Specific Gravity is 2.7
  • Streak is white.
  • Associated Minerals are numerous and include many exotic species: Schizolite, murmanite, aegirine, natrophosphate, kalifersite, djerfisherite, vitusite-(Ce), albite, lomonosovite, lueshite, serandite, nefedovite, fluorcaphite, lovozerite, ussingite, steenstrupine-(Ce), mangan-neptunite, eudialyte, sphalerite and villiaumite.
  • Notable Occurrences include the type locality; the eastern slope of Malyi Punkaruaiv Mountain in the Lovozero Massif of the Kola Peninsula, Russia as well as Langesundfjord, Norway; Ilimaussaq, Greenland and Mont Saint-Hilaire, Quebec, Canada.
  • Best Field Indicators include crystal habit, color, associations, locality and hardness.

 

THE MINERAL  CHLORARGYRITE

 

  • Chemistry: AgCl, Silver Chloride  
  • Class: Halides
  • Uses: As a minor ore of silver and as mineral specimens.
  • Specimens

Chlorargyrite, also called cerargyrite, is and/or was a locally important silver ore mineral. It forms isolated and fleetingly small but rich deposits of silver ore. It the western USA, many a ghost town sits near what was a rich and at least temporarily profitable chlorargyrite deposit. Several important chlorargyrite deposits are still being worked today.

The chlorargyrite forms on top of silver ore veins that have been subjected to weathering. The silver ore vein is often of such a concentration that it would not be a very profitable ore body were it not for a process called supergene enrichment. Supergene enrichment occurs when certain metals are leached out of slightly soluble minerals by hydrothermal fluids. These metals are then redeposited as a different mineral in concentrated pockets. These pockets are usually more rich in ore metals than the original material, thus the process is aptly termed an enrichment. Chlorargyrite is just one of these supergene enrichment product minerals.

Unfortunately for mineral collectors, chlorargyrite rarely forms good crystals. This makes the few crystals that are seen all the more valuable. Crystals are generally found as cubes that have a pearly gray to brown color and the luster is a generally silky to resinous.

 

PHYSICAL CHARACTERISTICS:

  • Color is colorless on fresh surfaces; pearly gray, brown or violet-brown otherwise.
  • Luster is resinous, silky or adamantine.
  • Transparency: Crystals are translucent to transparent.
  • Crystal System is isometric; 4/m bar 3 2/m.
  • Crystal Habits include very scarce cubes, more commonly massive, stalactitic, crusty and columnar.
  • Cleavage is absent.
  • Fracture is conchoidal.
  • Hardness is 1.5 - 2.5
  • Specific Gravity is 5.5 - 5.6 (very heavy for translucent minerals)
  • Streak is white.
  • Other Characteristics: Crystals darken upon exposure to light and plastic, ductile and sectile, meaning it can be molded, pounded into different shapes and cut into slices.
  • Associated Minerals include barite, calcite, stephanite, acanthite, native silver and other silver ore minerals.
  • Notable Occurrences include Atacama, Chile; Harz Mountains, Germany; Treasure Hill and Comstock Lode, Nevada, Colorado and Silver City District, Idaho, USA; Bolivia; France; Italy; Spain and New South Wales, Australia.
  • Best Field Indicators are color, luster, lack of cleavage, density, associations, ductility and crystal habit.

 

 

THE MINERAL CHLORITE

 


Chlorite is a general name for several minerals that are difficult to distinguish by ordinary methods. These minerals are all apart of the Chlorite Group of minerals. The chlorites are often, but not always considered a subset of the larger silicate group, The clays.

The general formula for chlorite is (Fe, Mg, Al)6(Si, Al)4O10(OH)8. However there are several different minerals that are apart of the chlorite group of minerals. The above formula is only a generalization of the more common members of this group. In order to see a list of most of the chlorite group minerals with their respective formula, see the discussion of the Chlorite Group.

For practical reasons most of the chlorites will be considered here as a single mineral, chlorite. Chlorites are generally green and crystallize in the monoclinic symmetry system. They all have a basal cleavage due to their stacked structure. Chlorites typically form flaky microscopic crystals and it is this reason that they are sometimes included in the clay group of minerals. However chlorites also form large individual tabular to platy crystals that are unlike most of the other clay minerals.

Chlorites are most often known to mineral collectors as inclusions in or coatings on quartz, danburite, topaz, calcite and many other minerals. The inclusions are usually a very strong green color despite the small amount of material that actually constitutes the inclusion. These inclusions and coatings can be an enhancement but are more often a bane to what might have been a really valuable mineral specimen.

The chlorite inclusions in clear quartz are particularly interesting when they form as a coating on a crystal early in its development. Because if the crystal later grows larger, ie. out and around the chlorite coating, the effect will be to produce a phantomed crystal. A phantom is a crystal that appears to have a smaller crystal inside of it. Many times the interior "crystal" is indistinct or ghostly and thus the name phantom.

There are many minerals that make up the chlorites and thus many varieties. One variety is called kaemmererite and is a variety of the chlorite clinochlore. Sometimes kaemmererite is called chromian clinochlore because of the increase chromium content. It is the chromium that gives kaemmererite its bright lavender to deep crimson red color.

THE PHYSICAL CHARACTERISTICS OF CHLORITE:

  • Color is usually green but can also be white, yellow, red, lavender and black.
  • Luster is vitreous, dull or pearly.
  • Transparency: Crystals are translucent transparent.
  • Crystal System is monoclinic; 2/m.
  • Crystal Habits: Rarely in large individual barrel or tabular crystals with an hexagonal outline. Usually found as alteration products of iron-magnesium minerals and as inclusions in other minerals. Aggregates can be scaly, compact, platy and as crusts.
  • Cleavage is perfect in one direction, basal; not seen in massive specimens.
  • Fracture is lamellar.
  • Hardness is 2 - 3
  • Specific Gravity is variable from 2.6 - 3.4 (average to slightly above average)
  • Streak is pal green to gray or brown.
  • Other Characteristics: Cleavage flakes are flexible but not elastic.
  • Associated Minerals include garnets, biotite, quartz, magnetite, talc, serpentine, danburite, topaz and calcite, among many others.
  • Notable Occurrences include Transvaal, South Africa; Zermatt, Switzerland; Guleman, Turkey; Lancaster Co., Pennsylvania, Brewster, New York; San Benito Co., California, USA and many other locallities world wide.
  • Best Field Indicators color, cleavage, associations and crystal habits.

THE MINERAL CHONDRODITE

 


Chondrodite is the most common and most well known member of the Humite Group of minerals. Members of the Humite Group are noted for having a mixture of silicate layers and oxide layers in their structures. The silicate layers have the same structure as olivine. The oxide layers have the same structure as brucite. In the case of chondrodite, there are two consecutive olivine layers that alternate between each brucite layer. The mineral humite, the next most common member of the group and the group's namesake, has three olivine layers between each brucite layer.

Chondrodite is not a particularly common mineral and is never seen in abundance. It is found in hydrothermal deposits and contact and regionally metamorphosed dolomitic limestones, most notably skarn deposits and in some serpentinite rocks. Crystals when found are very complex with many competing forms adding many different and seemingly unrelated faces. Most often the individual crystals appear rounded or granular. This characteristic of individual grains lead to its name which is derived from a Greek word that means, "grain".

 

PHYSICAL CHARACTERISTICS:

  • Color is commonly yellow, but also brown, reddish brown and red.
  • Luster is bright vitreous to resinous.
  • Transparency: Crystals are translucent with some unusual specimens being transparent.
  • Crystal System: Monoclinic; 2/m
  • Crystal Habits include stubby prismatic to tabular or rounded crystals, but as is most commonly the case, as embedded grains. Good crystals show multiple facets without discernible symmetry. Also found massive.
  • Cleavage is good in one direction, basal, (not always discernible however).
  • Fracture is subconchoidal.
  • Hardness is 6 - 6.5
  • Specific Gravity is 3.1 - 3.2
  • Streak is white.
  • Other Characteristics: Twinning may be seen as lamellar striations and some specimens display yellow fluorescence.
  • Associated Minerals include magnetite, diopside, spinel , pyrrhotite, graphite , humite, , wollastonite, monticellite , phlogopite, biotite, serpentine, clinochlore, olivine and calcite.
  • Notable Occurrences are include Monte Somma, Mount Vesuvius, Italy; Paragas, Finland; Kafveltorp, Sweden; and Franklin, New Jersey; Tilly Foster Mine, Brewster, New York; Riverside County, California and Arizona, USA.
  • Best Field Indicators are crystal habit, color, luster, cleavage, environment of formation and hardness.

 

THE MINERAL CHROMITE

 

  • Chemical Formula: FeCr2O4, Iron Chromium Oxide.
  • Class: Oxides and Hydroxides
  • Group: Spinel
  • Uses: The principle ore of chromium, as a refractory component, as a dye and as mineral specimens.
  • Specimens
Chromite is the most important ore of chromium from which it derives its name. Chromium is an important metal and has a wide range of industrial uses.

Chromite forms in deep ultra-mafic magmas and is one of the first minerals to crystallize. It is because of this fact that chromite is found in some concentrated ore bodies. While the magma is slowly cooling inside the Earth's crust, chromite crsytals are forming and because of their density, fall to the bottom and are concentrated there.

Although its primary origin is ultra-mafic rocks such as peridotites, chromite is also found in metamorphic rocks such as serpentites. Chromite, as is indicated by its early crystallization is resistant to the altering affects of high temperatures and pressures. Thus it is capable of going through the metamorphic processes unscathed, while other minerals around it are being altered to serpentine, biotite and garnets. This characteristic also explains chromites use as a refractory component in the bricks and linings of blast furnaces.

Usually magnesium is present in chromite substituting for the iron and in fact a solid solution series exists between chromite and the much rarer mineral magnesiochromite. All chromite specimens in nature contain some magnesium, likewise all natural magnesiochromites contain some iron. Magnesiochromite is grayer in color and in streak and has a slightly lower density than chromite at a specific gravity of 4.2 to 4.4.

 

PHYSICAL CHARACTERISTICS:

  • Color is brownish black to a deep dark black.
  • Luster is metallic to greasy.
  • Transparency: Crystals are opaque.
  • Crystal System is isometric; 4/m bar 3 2/m
  • Crystal Habits include octahedrons often with dodecahedral faces modifing the edges of the octahedron to the point of rounding the crystal. Well formed crystals are rare and chromite is usually found massive or granular.
  • Cleavage is absent.
  • Fracture is conchoidal.
  • Hardness is 5.5
  • Specific Gravity is 4.5 - 4.8 (average for metallic minerals)
  • Streak is brown.
  • Other characteristics: Weakly magnetic and an octahedral parting is sometimes seen.
  • Associated Minerals include olivine, talc, serpentine, uvarovite, pyroxenes, biotite, magnetite and anorthite.
  • Notable Occurrences include several mines in North Carolina, Montana, Maryland, Oregon, Texas, California and Wyoming, USA also found in Turkey; South Africa; Philippines and Russia.
  • Best Field Indicators are crystal habit, streak, associations with ultra-basic minerals and parting.

THE MINERAL CHROMIUM

 


Chromium rarely occurs naturally in its elemental form and has never been used as an ore of itself. However some native uncombined chromium has been discovered and therefore chromium is recognized as a mineral. The first specimens are attributed to the type locality in Sichuan, China, but the Udachnaya (Lucky) Mine in Russia produces more reliable examples. The Udachnaya is a Kimberlite pipe rich in diamonds. The reducing environment of the kimberlite helped to produce the elemental chromium and diamond. Chromium is related to two chromium and iron alloys: Ferchromide; Cr3Fe0.4 and chromferide; Fe3Cr0.4. Both minerals are structurally similar to chromium.
As an element, chromium is very useful. Its name comes from the Greek word for color, chroma. This is a good name for chromium, for it is one of the strongest coloring agents known. Numerous minerals owe their colors to chromium either from chromium being an important part of their chemistry or just as a trace. Chromium gives ruby its red and emerald its green. A little chromium goes a long way! The small list of chromium colored minerals in the table below demonstrates this well.


Chromium
in the formula:

Chromium
as a trace:

Industrially, chromium is used for a host of purposes. It is considered a strategic metal and is used in alloys for hardening and corrosion resistance. Its various compounds are used for a variety of colors in paints and glass. Some chromium chemicals are also used as oxidizers and for many other uses. Most chromium is extracted from the ore mineral chromite and some from crocoite.

 

PHYSICAL CHARACTERISTICS:

  • Color is white.
  • Luster is metallic.
  • Transparency: Specimens are opaque.
  • Crystal System is isometric; 4/m bar 3 2/m.
  • Crystal Habits are limited to granular specks and labratory grown specimens.
  • Hardness is 4
  • Specific Gravity is 7.21 (heavy for a metallic mineral).
  • Associated Minerals include diamond, spinel, copper and iron.
  • Notable Occurrences include the type locality in Sichuan, China as well as the Udachnaya (Lucky) pipe, Yakutia, Russia.
  • Best Field Indicators are color, locality, hardness and density.

 

THE MINERAL CHRYSOBERYL

 

Also see variety specimens:

Chrysoberyl is a poorly known mineral in the gem world even though the gem varieties are popular.
There are three main gem varieties:
  • The first type is simply faceted transparent Chrysoberyl that is usually found in yellowish green to green, yellow and shades of brown. It is a fine gemstone, but is over-shadowed by its two cousins.
  • The second variety is the "cat's eye", also known as cymophane. The effect is caused by microscopic needle-like inclusions that reflect light into a single dynamic sliver of light running along the center of the crystal thus making it look like a living cat's eye! Although other minerals such as tourmalines, scapolite, corundum, spinel and quartz form "cat's eye" stones, they must be designated as "tourmaline cat's eye", or "ruby cat's eye" in the jewelry industry. Only chrysoberyl can be referred to as "cat's eye" with no other designation.
  • The third and perhaps most interesting is Alexandrite. This rare and valuable gemstone has the unique property of changing color depending on the type of light that hits it. In sunlight, it appears almost emerald green, while in artificial incandescent light it appears a violet-red. Some sapphires show similar ability, and synthetic sapphires are now on the market being sold as "Alexandrites" but at substantially lower prices than natural Alexandrite.

The most interesting natural uncut crystals of chyrsoberyl are the cyclic twins called "trillings." These crystals appear hexagonal but are the result of a triplet of three "twins," with each "twin" taking up 120 degrees of the cyclic trilling.

 

 

 

 

PHYSICAL CHARACTERISTICS:

  • Color is yellow, green and brown.
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits: Crystals tend to be blocky and are often distorted by twinning effects that sometimes produce a psuedo-hexagonal cyclic twin. also granular.
  • Cleavage is fair in one direction and poor in another.
  • Fracture is conchoidal.
  • Hardness is 8.5
  • Specific Gravity is 3.7+ (above average for translucent minerals)
  • Streak is white.
  • Associated Minerals include garnet, mica and feldspars.
  • Other Characteristics: Pleochroic (different colors seen from different viewing angles), high refractive index (around 1.75).
  • Notable Occurrences include the Ural Mountains, Russia, Sri Lanka, Brazil, and Burma.
  • Best Field Indicators include possible presence of twinned crystals, color, great hardness, and poor cleavage. 
 

THE MINERAL CHRYSOCOLLA

 


Chrysocolla is attractive blue-green that provides a unique color to the mineral world. Chyrsocolla is perhaps more appropriately a mineraloid than a true mineral. Most of the time it is amorphous meaning that it does not have a coherent crystalline structure. However at higher temperatures it does demonstrate a distorted crystal structure that seems to be composed of Si4 O10 sheets. Chrysocolla forms in the oxidation zones of copper rich ore bodies.

Pure chrysocolla is soft and fragile and therefore not appropriate for use in jewelry. However, chrysocolla often is "agatized" in chalcedony quartz and it is the quartz that provides the stone with its polish and durability. Druzy Chrysocolla is a rock composed of agatized chysocolla with a crust of small sparkling quartz crystals in small cavities. A skilled craftsman, if able to polish a specimen that accentuates the colored swirles of chrysocolla and sparkles of the druzy quartz, can produce a lovely and valuable piece of jewelry. Occasionally, chrysocolla can have a turquoise color and be used as a fraudulent substitute for the more precious stone.

 

PHYSICAL CHARACTERISTICS:

  • Color is a unique green-blue but can vary widely from more blue to more green, often in the same specimen.
  • Luster is earthy to dull or vitreous and waxy.
  • Transparency specimens are translucent to opaque.
  • Crystal System is probably monoclinic or orthorhombic.
  • Growth Habits include mostly massive forms that can be crusts, stalachtites and botryoidal. Also as inclusions in other minerals such as quartz.
  • Cleavage is absent.
  • Fracture is pronounced conchoidal.
  • Hardness is variable from 2 to 4.
  • Specific Gravity is approximately 2.0 - 2.3 (very light)
  • Streak is white to blue-green.
  • Associated Minerals are quartz, limonite, azurite, malachite, cuprite and other secondary copper minerals.
  • Other Characteristics: may have an opal like appearance.
  • Notable Occurrences include Arizona, Utah, New Mexico and Pennsylvania, USA; Isreal; Zaire and England.
  • Best Field Indicators are lack of crystals, color, fracture, low density and softness. 
 

THE MINERAL SERPENTINE

 

  • Chemistry: (Mg,Fe)3Si2O5(OH)4, Magnesium Iron Silicate Hydroxide
  • Class: Silicates
  • Subclass: phyllosilicates
  • Group: Kalolinite-Serpentine
  • Uses: many industrial applications, including brake linings and fireproof fabrics and as an ornamental stone.
  • Specimens

Serpentine is a major rock forming mineral and is found as a constituent in many metamorphic and weather igneous rocks. It often colors many of these rocks to a green color and most rocks that have a green color probably have serpentine in some amount.
Serpentine is actually a general name applied to several members of a polymorphic group. These minerals have essentially the same chemistry but different structures. The following is a list of these minerals, their formulas and symmetry class:
  • Antigorite; (Mg,Fe)3Si2O5(OH)4; monoclinic.
  • Clinochrysotile; Mg3Si2O5(OH)4; monoclinic.
  • Lizardite; Mg3Si2O5(OH)4; trigonal and hexagonal.
  • Orthochrysotile; Mg3Si2O5(OH)4; orthorhombic.
  • Parachrysotile; (Mg,Fe)3Si2O5(OH)4; orthorhombic.

Their differences are minor and almost indistinguishable in hand samples. However, the chrysotile minerals are more likely to form serpentine asbestos, while antigorite and lizardite form cryptocrystalline masses sometimes with a lamellar or micaceous character. Asbestos had been used for years as a fire retarding cloth and in brake linings. Its links to cancer however has led to the development of alternative materials for these purposes.

Serpentine's structure is composed of layers of silicate tetrahedrons linked into sheets. Between the silicate layers are layers of Mg(OH)2. These Mg(OH)2 layers are found in the mineral brucite and are called brucite layers. How the brucite layers stack with the silicate layers is the main reason for the multiple polymorphs. The stacking is not perfect and has the effect of bending the layers. In most serpentines, the silicate layers and brucite layers are more mixed and produced convoluted sheets. In the asbestos varieties the brucite layers and silicate layers bend into tubes that produce the fibers.

Serpentine can be an attractive green stone that takes a nice polish and is suitable for carving. It has been used as a substitute for jade and is sometimes difficult to distinguish from jade, a testament to the beauty of finer serpentine material.

Non-fiberous serpentine is not a cancer concern. Asbestos serpentines should be kept in closed clear containers, but makes an attractive specimen. Sometimes with a golden color as the name chrysotile in greek means golden fibers.

 

PHYSICAL CHARACTERISTICS:

  • Color is olive green, yellow or golden, brown, or black.
  • Luster is greasy, waxy or silky.
  • Transparency crystals are translucent and masses are opaque.
  • Crystal System is variable, see above.
  • Crystal Habits: never in large individual crystals, usually compact masses or fibrous. Veins of viberous serpentine can be found inside of massive serpentine or other rocks.
  • Cleavage the varieties of crysotile have none, in lizardite and antigorite it is good in one direction.
  • Fracture is conchoidal in antigorite and lizardite and splintery in the crysotiles.
  • Hardness is 3 - 4.5
  • Specific Gravity is 2.2 - 2.6
  • Streak white
  • Associated Minerals include chromite, olivine, garnets, calcite, biotite and talc.
  • Other Characteristics: serpentine in the rough has a silky feel to the touch and fibers are very flexible.
  • Notable Occurances Val Antigorio, Italy; Russia; Rhodesia Switzerland; North Carolina, California, Rhode Island and Arizona, USA and Quebec, Canada.
  • Best Field Indicators softness, color, silky feel and luster, asbestos if present and its flexibility.

 

THE MINERAL CHURCHITE-(Y)

 

  • Chemistry: (Y, Er)PO4 - 2H2O, Hydrated Yttrium Erbium Phosphate.
  • Class: Phosphates
  • Uses: as a very minor ore of yttrium and erbium and as mineral specimens.
  • Specimens

Churchite-(Y), also known as just churchite and weinschenkite, is a fairly scarce rare earth phosphate. A rare earth mineral is one that contains any of the so called rare earth metals/elements. In this case, it is yttrium and erbium, two industrially valuable metals that are the two rare earth elements in churchite-(Y). The (Y) is for the yttrium which is more significant than the erbium in the chemistry of churchite-(Y). The mineral churchite-(Nd) contains the element Neodymium, another rare earth element.

These are some other rare earth phosphates and their respective chemistries:
    • Florencite (Cerium Aluminum Phosphate Hydroxide)
    • Monazite (various rare earth metals Phosphate)
    • Rhabdophane (Hydrated Cerium Lanthanum Neodymium Yttrium Phosphate)
    • Xenotime (Yttrium Phosphate)

In most of Europe the mineral churchite-(Y) is known as weinschenkite and is named for a famous German mineralogist. Specimens of churchite form interesting cotton-white sprays of fine acicular or hair-like clusters. The sprays are unique and unlike other minerals that form acicular crystals. Although quite hard to describe, the clusters simply must be seen in order to appreciate their unusual character.

 

PHYSICAL CHARACTERISTICS:

  • Color is white, colorless or gray.
  • Luster is silky to vitreous.
  • Transparency: Specimens are translucent.
  • Crystal System is monoclinic.
  • Crystal Habits include sprays of fine acicular or hair-like clusters also as fibrous crusts and rosettes.
  • Cleavage is perfect but usually not discernible.
  • Fracture is fibrous.
  • Hardness is 3.
  • Specific Gravity is approximately 3.3 (slightly above average for translucent minerals)
  • Streak is white.
  • Other Characteristics: Maybe slightly radioactive.
  • Associated Minerals include limonite, cacoxenite, beraunite and other phosphate minerals.
  • Notable Occurrences are limited to Rockbridge County, Virginia, USA; Auerbach, Germany and Cornwall, England.
  • Best Field Indicators are crystal habit, color, luster, associations and locality.

 

THE MINERAL CINNABAR

 


Cinnabar is a colorful mineral that adds a unique color to the mineral color palette. Its cinnamon to scarlet red color can be very attractive. Well shaped crystals are uncommon and the twinned crystals are considered classics among collectors. The twinning in cinnabar is distinctive and forms a penetration twin that is ridged with six ridges surrounding the point of a pryamid. It could be thought of as two scalahedral crystals grown together with one crystal going the opposite way of the other crystal. Cinnabar was mined by the Roman Empire for its mercury content and it has been the main ore of mercury throughout the centuries. Some mines used by the Romans are still being mined today. Cinnabar shares the same symmetry class with quartz but the two form different crystal habits.

 

PHYSICAL CHARACTERISTICS:

  • Color is a bright scarlet or cinnamon red to a brick red.
  • Luster is adamantine to submetallic in darker specimens.
  • Transparency crystals are translucent to transparent.
  • Crystal System is trigonal; 32
  • Crystal Habits: individual, well formed, large crystals are scarce; crusts and crystal complexes are more common; may be massive, or in capilary needles. Crystals that are found tend to be the six sided trigonal scalahedrons that appear to have opposing three sided pyramids. It also forms modified rhombohedrons, prismatic and twinned crystals as discribed above.
  • Cleavage is perfect in three directions, forming prisms.
  • Fracture is uneven to splintery.
  • Hardness is 2 - 2.5.
  • Specific Gravity is approximately 8.1+ (very heavy for a non-metallic mineral)
  • Streak is red
  • Associated Minerals are realgar, pyrite, dolomite, quartz, stibnite and mercury.
  • Other Characteristics: silghtly sectile and crystals can be striated.
  • Notable Occurances include Almaden, Spain; Idria, Serbia; Hunan Prov., China and California, Oregon, Texas, and Arkansas, USA.
  • Best Field Indicators are crystal habit, density, cleavage, softness and color.

 

THE MINERAL CLAUSTHALITE

 

  • Chemistry: PbSe, Lead Selenide
  • Class: Sulfides
  • Subclass: Selenides
  • Group: Galena
  • Uses: As a very minor ore of lead and selenium and as mineral specimens.
  • Specimens

Clausthalite is a member of the Galena Group of minerals. Its properties are very similar to galena as it shares basically the same structure. However it can be distinguished from the far more common galena by its greater density and lack of good crystals. The two minerals are in a series in which the sulfur and selenium ions substitute for each other.

Clausthalite and the mineral crookesite, a copper thallium selenide are the two most common selenium minerals. However they are not ores of selenium due to their rarity and the fact that selenium is mostly acquired through the processing of copper sulfide ores. The selenium is found as a trace in many copper sulfide minerals especially pyrite and in coal. Some other selenide minerals that contain a significant amout of selenium include:
  • Berzelianite (Copper Selenide)
  • Eucairite (Silver Copper Selenide)
  • Hakite (Copper Mercury Silver Antimony Selenium Sulfide)
  • Klockmannite (Copper Selenide)
  • Naumannite (Silver Selenide)
  • Penroseite (Nickel Selenide)
  • Palladseite (Palladium Selenide)
  • Tiemannite (Mercury Selenide)
  • Umangite (Copper Selenide)
The element selenium is used in the production of photoelectric cells, resisters, photographic chemicals, pigments and many other industrial uses.

 

PHYSICAL CHARACTERISTICS:

  • Color is a bright lead gray, blue gray to gray black.
  • Luster is metallic.
  • Transparency: Crystals are opaque.
  • Crystal System: Isometric; 4/m bar 3 2/m.
  • Crystal Habits include rare cubic and octahedral crystals; much more commonly found in massive and granular forms.
  • Cleavage: perfect in three directions forming cubes.
  • Fracture: Uneven.
  • Hardness is 2.5.
  • Specific Gravity is 8.1 - 8.3 (much heavier than average for metallic minerals)
  • Streak is black.
  • Associated Minerals include gold, pyrite, calcite, epidote, selenium, sphalerite, tiemannite, naumannite, penroseite, galena and other sulfides.
  • Notable Occurrences include the type locality of the Lorenz Mine, Clausthal, Harz, Germany as well as Corvusite Mine, Montrose County, Colorado and San Miguel County, New Mexico, USA; Slavkovice, Central Moravia, Czech Republic; Falun, Sweden and Lake Athabasca, Saskatchewan, Canada.
  • Best Field Indicators are crystal habit, perfect cubic cleavage, associations and density.

 

THE MINERAL CLIFFORDITE

 


Cliffordite is named after mineralogist Clifford Frondel who also has given his name to the phosphate mineral frondelite. Cliffordite is a very rare tellurium mineral. The type locality for cliffordite, the San Miguel Mine and other mines of Moctezuma, Sonora, Mexico, is famous for rare telllurium minerals. The symmetry of cliffordite is the unusual bar 3 2/m of the Diploidal Class. A class of symmetry that contains the sulfide mineral pyrite, among others. Cliffordite is a radioactive mineral and should be stored away from minerals that are affected by radioactivity and of course human exposure should be limited.

 

THE PHYSICAL CHARACTERISTICS:

  • Color is bright yellow to sulfur yellow.
  • Luster is adamantine.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is isometric; bar 3 2/m.
  • Crystal Habits include small octahedral crystals.
  • Hardness is 4.
  • Specific Gravity is approximately 6.6 - 6.7 (very heavy for translucent minerals).
  • Streak is bright yellow.
  • Other Characteristics: Specimens are slightly radioactive.
  • Associated Minerals include tellurium and other tellurates and tellurites.
  • Notable Occurrences are limited to the type locality of San Miguel Mine, Moctezuma, Sonora, Mexico.
  • Best Field Indicators are locality,softness, high density, luster, radioactivity and cleavage.

 

 

THE MINERAL CLINOCHLORE

 


Clinochlore is one of the more common members of the Chlorite Group of minerals. These minerals are all difficult to differentiate by ordinary means and often the general mineral name chlorite is given to specimens that lack distinguishing characterics. Clinochlore forms from the metamorphic and hydrothermal alterations of other iron and magnesium silicate minerals. Clinochlore gets its name from the Greek words for inclined and green since its structure is monoclinic and its common color is green.

Clinochlore forms a series with the mineral chamosite. Chamosite is the iron rich equivalent of clinochlore. Their properties are only slightly different with chamosite being darker and less transparent than clinochlore. A chromium rich variety of clinochlore is known as kaemmererite and is quite beautiful and wonderfully colored bright lavender to crimson.

 

PHYSICAL CHARACTERISTICS:

  • Color is usually green to an emerald green but also red, brown, tan, yellow or white.
  • Luster is vitreous to pearly.
  • Transparency: Crystals are translucent to transparent.
  • Crystal System is monoclinic; 2/m.
  • Crystal Habits include pseudohexagonal tabular crystals with tapering pyramidal terminations. Commonly foliated, fibrous, granular, earthy, massive. Twinning is seen on some larger specimens.
  • Cleavage is perfect in one direction, basal.
  • Fracture is uneven.
  • Hardness is 2 - 2.5
  • Specific Gravity is 2.6 - 3.0 (average).
  • Streak is greenish white or white.
  • Other Characteristics: Cleavage flakes are flexible but inelastic.
  • Associated Minerals include pyrite, quartz, dolomite, fluorapatite, gmelinite, rutile, siderite, albite, anatase, calcite, catapleiite, talc, chlorite, sphalerite, serpentine, actinolite, biotite, tainiolite, olivine, plagioclase, chromite and uvarovite.
  • Notable Occurrences including the type locality of West Chester, Chester County, Pennsylvania, USA as well as The Tilly Foster mine, New York; Pima and Yavapai Counties, Arizona; New Idria district, San Benito County, California and Franklin and Sterling Hill, New Jersey, USA; Tirol, Austria; Val Malenco, Lombardy and Ala, Piedmont, Italy; near Zermatt, Valais, Switzerland; Spain; Shetland Islands, Scotland; Kop Daglari, Erzurum, Turkey; Ural Mountains, Russia and most localities from where chlorite is found.
  • Best Field Indicators are crystal habit, softness, color and cleavage.

 

 

THE MINERAL CLINOCLASE

 

  • Chemistry: Cu3AsO4(OH)3, Copper Arsenate Hydroxide.
  • Class: Phosphates
  • Uses: mineral specimens
  • Specimens

Clinoclase is a rare secondary copper mineral. It was first known from the Wheal Gorland Mine (now closed), a producer of many fine, rare and world-reknowned secondary minerals. Clinoclase has a beautiful dark blue to dark greenish blue color. Although usually small, its crusts of acicular crystals make for very attractive specimens as they coat all the nooks and crevices of a fractured host rock. A specimen of clinoclase is a pleasure to own by any serious collector of rare minerals.

 

PHYSICAL CHARACTERISTICS:

  • Color is dark blue and with shades of green.
  • Luster is vitreous.
  • Transparency: specimens are translucent.
  • Crystal System: is monoclinic; 2/m
  • Crystal Habits include acicular crystals in radiating and near botryoidal crusts. Individual crystals of any size are rare, but when found are tabular or prismatic with small triangular faces modifying the crystals.
  • Cleavage is good in one direction.
  • Fracture is lamellar.
  • Hardness is 2.5 - 3
  • Specific Gravity is approximately 4.3 (heavy for translucent minerals)
  • Streak is bluish green.
  • Associated Minerals are malachite, olivenite, quartz, limonite, adamite, azurite, brochantite and other rare secondary copper ore minerals.
  • Other Characteristics: slightly soluable in hydrochloric acid.
  • Notable Occurrences: Cornwall, England; Libethen, Romania; Zaire; Russia; California, Utah and Arizona, USA.
  • Best Field Indicators: color, streak, crystal habits, associations and density.

 

 

THE MINERAL CLINOHUMITE

 

  • Chemistry: Mg9(SiO4)4(F, OH)2, Magnesium Silicate Fluoride Hydroxide.
  • Class: Silicates
  • Subclass: Nesosilicates
  • Group: Humite
  • Uses: rarely cut as a gemstone and as mineral specimens.
  • Specimens

Clinohumite is a mineral found as small grains in the marbles of contact metamorphic environments. It was first discovered in the metamorphosed limestone blocks that were ejected by the volcano Mt. Vesuvius, near Napoles, Campania, Italy. Clinohumite is a fluorescent mineral and will glow a tan to yellow-orange color when subjected to shortwave UV light. It is similar in fluorescent color to the bright humite material found at Franklin, New Jersey. Humite is a related species to clinohumite as might be expected by their names. Clinohumite is named in allusion to its monoclinic symmetry as opposed to humite's orthorhombic symmetry. Clinohumite's structure is often intergrown with humite's structure in the same crystal. Clinohumite from Pamir Mountains, Tadzhikistan, Russia has been cut as a brilliant yellow-orange gemstone, but it is rare and sought after only by collectors.

Clinohumite, like humite, is a member of the Humite Group of minerals. Members of the Humite Group are noted for having a mixture of silicate layers and oxide layers in their structures. The silicate layers have the same structure as olivine. The oxide layers have the same structure as brucite. Clinohumite has four stacked olivine layers that alternate between the brucite layers. The formula could be written as:
(Mg2SiO4)4 - Mg(F, OH)2

This formula distinguishes the chemistry of the two types of layers. The most common member of the Humite Group is chondrodite which has two olivine layers between each brucite layer. Humite, the namesake of the group, has three.

 

PHYSICAL CHARACTERISTICS:

  • Color is yellow, red, brown or orange.
  • Luster is vitreous to resinous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System: Monoclinic; 2/m.
  • Crystal Habits include small prismatic to rounded crystals, but as is most commonly the case, as embedded indistinct grains. Lamellar twinning is common.
  • Cleavage is poor in one direction, basal.
  • Fracture is subconchoidal.
  • Hardness is 6.
  • Specific Gravity is 3.2 - 3.4
  • Streak is white.
  • Other Characteristics: Many specimens (usually those that are of a lighter color) fluoresce a yellow-orange color under shortwave UV light. Crystals are pleochroic from yellow to colorless.
  • Associated Minerals include humite, talc, geikielite, lazurite, dolomite and calcite.
  • Notable Occurrences include the type locality of Mt. Vesuvius, near Napoles, Campania, Italy as well as the Pamir Mountains, Tadzhikistan, Russia; Pargas, Finland; Llanos de Juanar, Malaga, Spain; Tilly Foster Mine, New York; Fort Defiance, Apache County, Arizona; Crestmore Quarry, Riverside County and Lower Lake, Fresno County, California; Luna, New Mexico and Franklin, New Jersey, USA.
  • Best Field Indicators are color, associations, fluorescence, environment of formation and hardness. 
 

COBALT

 


Cobalt has yet to be found in nature, but is being grown in labratories and these cobalt specimens are starting to appear in rock shops. Since it has never been found in nature it is technically not a mineral although lab grown specimens can look like a natural stone.

The element cobalt has many industrial uses especially in dyes and in magnets. As a dye, cobalt produces a spectacular blue color that is used most noteably in glass and ceramics. When alloyed with iron and nickel, cobalt produces a strong magnet. Cobalt has many uses in certain alloys for airplane parts and engines.

 

PHYSICAL CHARACTERISTICS:

  • Color is steel grey.
  • Luster is metallic.
  • Transparency: Specimens are opaque.
  • Crystal System is isometric.
  • Crystal Habits include only lab grown specimens.
  • Specific Gravity is 8.9 (very heavy for a metallic mineral).
  • Other Charateristics: Magnetic.
  • Notable Occurrences include only lab grown specimens.
  • Best Field Indicators are color, magnetism and density.

 

THE MINERAL COBALTITE

 


Cobaltite although rare is still an important and valuable ore of cobalt, a strategically and industrially useful metal. The symmetry of cobaltite is somewhat in dispute. Its structure is very similar to the structure of pyrite, FeS2. The sulfur to sulfur link (S-S) in pyrite is replaced by an arsenic to sulfur link (As-S) in cobaltite. If the position of the arsenic is not ordered then the symmetry is the same as pyrite's symmetry which is in the isometric class, 2/m bar 3. However it appears from some x-ray spectroscopy studies that the arsenic is ordered there by breaking the higher symmetry and giving cobaltite a symmetry of the orthorhombic class, 2/m 2/m 2/m. But the debate is not settled yet.

Regardless of its actual symmetry, cobaltite forms isometric looking crystals. Either from really being isometric or from simply having such a similar structure to pyrite, cobaltite's crystals mimic those of pyrite. Although the crystal habits are similar to pyrite, cobaltite can not be confused with pyrite which is brassy yellow in contrast to cobaltite's silver gray or white color. Skutterudite on the other hand is also white and forms similar crystals although it has poor cleavage.

Often deposits of cobaltite will have a weathering crust of minerals such as erythrite, Co3(AsO4)2-8(H2O). Since cobalt is a strong coloring metal, minerals like erythrite are strongly colored, in this case a pink to bright purple. Miners called these colorful minerals "cobalt blooms" and used them as indicators of the presence of cobalt ores, such as cobaltite. Good crystals are usually common when cobaltite deposits are found and are a treasure for collectors.

 

PHYSICAL CHARACTERISTICS:

  • Color is white to silver gray.
  • Luster is metallic.
  • Transparency crystals are opaque.
  • Crystal System has been described as isometric; 2/m bar 3, but its actual structure is perhaps orthorhombic; m m 2 although the last word has not been said on this subject.
  • Crystal Habits include cubes, octahedrons, pyritohedrons and combinations of these isometric forms. If cobaltite is actually orthorhombic than these forms are either pseudocubes etc or they are pseudomorphs from a truly isometric phase which existed at higher temperature and/or pressure. Cobaltite is also commonly massive and granular.
  • Cleavage is distinct in three directions forming cubes.
  • Fracture is uneven to subconchoidal.
  • Hardness is 5.5
  • Specific Gravity is approximately 6.0 - 6.4+ (heavier than average for metallic minerals)
  • Streak is dark gray.
  • Other Characteristics: Striations on cube faces.
  • Associated Minerals are silver, chalcopyrite, pyrite, erythrite, skutterudite and other cobalt minerals.
  • Notable Occurrences include Cobalt, Ontario, Canada; Zaire; Siegerland, Germany; Skutterud, Norway; Tunaberg, Sweden; Sonora, Mexico; England; Boulder, Colorado and other USA localities.
  • Best Field Indicators are crystal habit, cleavage, color, streak, association with erythrite and luster. 
 

THE MINERAL COCONINOITE

 

  • Chemistry: Fe2Al2(UO2)2(PO4)4(SO4)(OH)2 - 20H2O , Hydrated Iron Aluminum Uranyl Phosphate Sulfate Hydroxide.
  • Class: Phosphates
  • Uses: a very minor ore of uranium and as mineral specimens.
  • Specimens

Coconinoite is a rare uranium mineral that is named for the type locality from where it was first described, Coconino Co., Arizona, USA. It is an extremely unusual mineral just by its chemistry alone. Not only does it have the uranyl groups in its chemistry but it also has a sulfate group. Coconinoite is interesting for its good fluorescence under UV light as well. Remember, this is also a radioactive mineral and should be stored away from other minerals that are affected by radioactivity and human exposure should always be limited.

 

PHYSICAL CHARACTERISTICS:

  • Colors are various shades of pale yellow.
  • Luster is vitreous or waxy to dull or earthy.
  • Transparency crystals are translucent.
  • Crystal System is orthorhombic or possibly monoclinic.
  • Crystal Habits include crusts, earthy masses, foliated and scaly aggregates.
  • Specific Gravity is approximately 2.9 (average for translucent minerals).
  • Streak is pale yellow.
  • Other Characteristics: radioactive and some specimens are fluorescent.
  • Notable Occurrence is Sun Valley Mine, Coconino Co., Arizona, USA.
  • Best Field Indicators are color, fluorescence if present, radioactivity and locality.

 

THE MINERAL COESITE

 

  • Chemistry: SiO2, Silicon Dioxide.
  • Class: Silicate
  • Group: Quartz.
  • Uses: As an indicator of high pressure crystallization (possibly a meteorite impact) and as mineral specimens.
  • Specimens

Coesite is a polymorph of quartz, meaning that it is composed of the same chemistry, SiO2, but has a different structure. Both quartz and coesite are polymorphs with all the members of the Quartz Group which also include cristobalite, tridymite and stishovite.

Well formed crystals are very rare as coesite does not usually get much time to form crystal faces. It forms quickly at high pressures, above 20 kilobars. Where on Earth do you find such an environment? At a meteor impact site! Where the pressures are great but the overall temperature is not that high. And indeed it was at the meteorite crater in Arizona, called Meteor Crater, one of the most well studied meteor impact sites in the world, that the first tiny crystals of coesite, and its cousin stishovite, were found in nature. Coesite was actually first synthesized in 1953 before the discovery at Meteor Crater. Now the presence of coesite and stishovite is diagnostic evidence of a meteor impact when craters of unknown origin are examined. Coesite has also been identified in kimberlites where other high pressure minerals such as diamond are found.

The structure of coesite is composed of SiO4 tetrahedrons that are linked into four membered rings. The rings are then linked together into a chain-like structure. This structure is much more compact than the other members of the quartz group, except stishovite, and is reflected in the higher density and index of refraction.

Coesite is only metastable at normal surface temperatures; meaning that, if it could, it would slowly convert to the quartz structure. But this is a slow and complicated process taking thousands of years if it happens at all. It is a slow process mostly because the transformation involves the breaking of bonds and the rearrangement of atoms.

 

 

PHYSICAL CHARACTERISTICS:

  • Color is colorless or white.
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is monoclinic; 2/m .
  • Crystal Habit includes always small (usually microscopic) and very rarely well formed prismatic crystals.
  • Cleavage information is unavailable.
  • Fracture is probably conchoidal.
  • Hardness is 8
  • Specific Gravity is 3.00+ (average for translucent minerals)
  • Streak is clear.
  • Other Characteristics: Refractive index is approximately 1.59
  • Associated Minerals include sanadine, diamond, garnets, pyroxenes, iron meteorites and stishovite.
  • Notable Occurrences include Canyon Diablo, Meteor Crater, Arizona, USA and other meteorite craters around the world as well as at Kimberly, South Africa.

  

THE MINERAL COLUMBITE

 

  • Chemical Formula: (Fe, Mn, Mg)(Nb, Ta)2O6, Iron Manganese Magnesium Niobium Tantalum Oxide.
  • Class: Oxides and Hydroxides
  • Uses: An ore of niobium and tantalum and as mineral specimens.
  • Specimens

Columbite is the most widespread niobium mineral and makes for an important ore of the industrially useful metal. Niobium, Nb, is used in alloys for improved strength. It also has shown superconductive properties and is being studied with other metals for a possible breakthrough alloy in this new industrial field. Niobium had been called columbium hence the name columbite. The official name was made niobium in the 1950's after a century of debate, although some groups still do not recognize the official name and still refer to it as columbite. Of course most geologists still refer to its name sake mineral as columbite instead of the proposed "niobite".

Columbite forms a series with the mineral tantalite. In fact the two are often grouped together as a semi-singular mineral called columbite-tantalite in many mineral guides. A series is where two or more elements can occupy the same places within a crystal structure and their respective percentages can then vary. Columbite is the more niobium rich end member and tantalite is the more tantalum rich end member. The two minerals of this series have similar properties since they have the same structure and similar chemistries (tantalum and niobium are very similar elements).
Tantalite's greatest difference from columbite is its much greater specific gravity, 8.0+ compared to columbite's 5.2. Other properties that vary slightly are color, transparency and streak. Both minerals can be found more or less together in granitic pegmatites rich in lithium and phosphorus minerals with columbite concentrated at the edges of the pegmatite and tantalite enriched in the core.

Columbite is a series within a series. The iron, manganese and magnesium amounts vary considerably without much effect on properties. However the end members are recognized as distinct minerals although collectors have found this to be rather cumbersome and generally prefer columbite to the non-unique names of ferrocolumbite, manganocolumbite and magnocolumbite.

As mineral specimens, columbite can be a nice addition to one's collection. Good crystals are both complex and handsome. Although the color selection is usually limited too black to brown the luster is generally good.

 

PHYSICAL CHARACTERISTICS:

  • Color is dark black, iron-black to dark brown.
  • Luster is submetallic.
  • Transparency: Crystals are nearly opaque being transparent in thin splinters.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include stubby prismatic crystals with complexly faceted or rounded terminations. Also very flat tabular crystals often aggregated together in parallel or nearly parallel groups. Can also be granular and massive.
  • Cleavage is good in one direction.
  • Fracture is subconchoidal.
  • Hardness is 6
  • Specific Gravity is approximately 5.0 to 5.3+ when near pure columbite (very heavy for non-metallic minerals).
  • Streak is brown to black.
  • Other Characteristics: Some specimens may demonstrate weak magnetism.
  • Associated Minerals include albite, spodumene, cassiterite, microcline, lepidolite, apatite, beryl, microlite, tourmalines and amblygonite.
  • Notable Occurrences include Newry, Maine; San Diego Co., California; Colorado and Amelia, Virginia, USA; Renfrow County, Ontario, Canada; Madagascar; Sweden; Norway; Brazil; Argentina; Kugi-Lyal, Pamir, Russia and Finland.
  • Best Field Indicators are crystal habit, streak, associations and specific gravity.

 

THE MINERAL CONICHALCITE

 

  • Chemistry: CaCuAsO4(OH), Calcium Copper Arsenate Hydroxide
  • Class: Phosphates
  • Subclass: Arsenates
  • Group: Adelite
  • Uses: A minor ore of copper and as mineral specimens.
  • Specimens

Conichalcite has a sparkling grass green color that once observed is hard to mistake for any other mineral. It is often encrusted onto limonitic rocks that have a red to yellow color and the two produce a very colorful specimen. Conichalcite forms in the oxidation zone of copper ore bodies. Oxygen rich ground water that might react with copper sulfide and/or copper oxide minerals produce a wonderful assortment of attractive and colorful minerals in a zone called the oxidation zone. Conichalcite is just one of these minerals. Other oxidation zone minerals include malachite, azurite, linnarite, etc.

Conichalcite forms a solid solution series with the mineral calciovolborthite. A solid solution series occurs when two or more structurally identical minerals can interchange elements within their chemistries without dramatically altering the crystal structure. In the case of conichalcite and calciovolborthite the two elements are arsenic and vanadium. Conichalcite is the arsenic rich end member of the series and calciovolborthite is the vanadium rich end member.

 

PHYSICAL CHARACTERISTICS:

  • Color is grass green to light green.
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is orthorhombic
  • Crystal Habits include the crusts of acicular to almost fibrous crystals. Also as botryoidal masses and compact crusts.
  • Cleavage is absent.
  • Fracture is uneven.
  • Hardness is 4.5
  • Specific Gravity is approximately 4.3 (heavy)
  • Streak is green.
  • Associated Minerals are limonite, malachite, beudantite, adamite, cuproadamite, olivenite and smithsonite.
  • Notable Occurrences include Juab Co., Utah, Nevada and Arizona, USA; Mexico; Chile; Poland and Zaire.
  • Best Field Indicators are crystal habit, color, associations and density.

 

THE MINERAL COPIAPITE

 

  • Chemistry: (Fe, Mg)Fe4(SO4)6(OH)2 - 20H2O, Hydrated Iron Magnesium Sulfate Hydroxide.
  • Class: Sulfates
  • Group: Copiapite
  • Uses: Only as mineral specimens.
  • Specimens

Copiapite is a secondary mineral that forms from the oxidation of iron sulfide deposits. At times it has been know to form rather quickly as a crust on exposed iron sulfide ore bodies at mines and sulfide rich coal dumps. It is named for the famed mineral locality at Copiapo, Chile which is where it was first discovered. It is difficult to distinguish copiapite from other similar hydrated iron sulfates without X-ray studies, however its confusion with yellow encrusted uranium minerals can be easily distinguished by its paler color, non-radioactivity and non-fluorescence. Specimens can be rather attractive, but they can lose water and should be stored in a closed container.

Copiapite lends its good name to a group of similar triclinic, hydrated, iron sulfates called the Copiapite Group. Although not a lot of creativity went into their names, the members of this group are all distinct minerals. The general formula of this group is AFe4(SO4)6(OH)2 - 20H2O, where A has a positive 2 charge and can be either magnesium, iron, copper, calcium and/or zinc. The formula can also be B2/3Fe4(SO4)6(OH)2 - 20H2O, where B has a positive 3 charge and can be either aluminum or iron.

These are the members of the Copiapite Group:
  • Aluminocopiapite (Hydrated Aluminum Iron Sulfate Hydroxide)
  • Calciocopiapite (Hydrated Calcium Iron Sulfate Hydroxide)
  • Copiapite (Hydrated Iron Magnesium Sulfate Hydroxide)
  • Cuprocopiapite (Hydrated Copper Iron Sulfate Hydroxide)
  • Ferricopiapite (Hydrated Iron Sulfate Hydroxide)
  • Magnesiocopiapite (Hydrated Magnesium Iron Sulfate Hydroxide)
  • Zincocopiapite (Hydrated Zinc Iron Sulfate Hydroxide)

THE PHYSICAL CHARACTERISTICS OF COPIAPITE:

  • Color is yellow, orange, sulfur-yellow, golden-yellow, greenish-yellow to ocher.
  • Luster is pearly to dull.
  • Transparency: Specimens are translucent to opaque.
  • Crystal System is triclinic: bar 1.
  • Crystal Habits include aggregates of small platy or scaly masses, encrustations and granular masses. Individual crystals are rare.
  • Cleavage is perfect in one direction.
  • Fracture is uneven.
  • Hardness is 3.5 - 3.
  • Specific Gravity is approximately 2.1 (light even for translucent minerals).
  • Streak is pale yellow.
  • Other Characteristics: Dissolves in water, is non-flourescent and has a metallic taste.
  • Associated Minerals include pyrite, other iron sulfides and other secondary minerals.
  • Notable Occurrences include Copiapo (hence the name), Atacama, Chile; France; Spain; Germany; Utah, California and Nevada, USA.
  • Best Field Indicators are solubility, density, color, non-flourescence and taste.

 

NATIVE COPPER

 

  • Chemistry: Cu, Elemental Copper
  • Class: Elements
  • Group: Gold
  • Uses: Minor ore of copper, ornamental stone
  • Specimens

Native copper (copper found in a chemically uncombined state) has been mined for centuries and now is all but depleted as an economically viable ore. Other copper minerals are far more economical to mine and purify into metallic copper that is used for wiring, electrical components, pennies and other coins, tubing and many other applications. Native copper is still found in limited quantities in once-active mining regions. These finds are now valuable as minerological specimens and ornamental pieces. Fine specimens only rarely demonstrate crystal faces and these are prized above otherwise similar specimens.

 

PHYSICAL CHARACTERISTICS:

  • Color is copper colored with weathered specimens tarnished green.
  • Luster is metallic.
  • Transparency is opaque.
  • Crystal System is isometric; 4/m bar 3 2/m
  • Crystal Habits include massive, wires and arborescent or branching forms as the most common, whole individual crystals are extremely rare but when present are usually cubes and octahedrons. Occasionally, massive forms will show some recognizable crystal faces on outer surfaces.
  • Cleavage is absent.
  • Fracture is jagged.
  • Streak is reddish copper color.
  • Hardness is 2.5-3
  • Specific Gravity is 8.9+ (above average for metallic)
  • Associated Minerals are silver, calcite, malachite and other secondary copper minerals.
  • Other Characteristics: ductile, malleable and sectile, meaning it can be pounded into other shapes, stretched into a wire and cut into slices.
  • Notable Occurrences include Michigan and Arizona, USA; Germany; Russia and Australia.
  • Best Field Indicators are color, ductility and crystal habit.

  

THE MINERAL CORDIERITE

 


Cordierite is not a well known or popular mineral for mineral collectors. However, its gemstone variety is well known and is rather popular among gemstone collectors and fanciers. The gemstone variety of cordierite is called iolite. Its unusual blue-violet color is attractive and is compared to a light blue sapphire with a purplish tint. It is the reason that cordeirite is sometimes called "water sapphire." One of the most notable characteristics of cordierite is its strong pleochroism, or color changing ability. When viewed from one direction, the crystal or gemstone may appear blue or blue-violet. But as the crystal or gemstone is rotated to another viewing direction, the color will appear yellowish gray to light blue. Many other minerals are pleochroic however most have such a small color change that it is not noticable by the human eye. Other minerals such as elbaite, show stronger pleochroism where changes in color shading can be discerned. Only a few minerals such as cordierite and the zoisite variety called tanzanite are extremely pleochroic and it is very easy to see the color changes. The strong pleochroism is the reason that cordierite and iolite are sometimes referred to by the synonym dichroite a greek word meaning two colored rock. Although cordeirite is actually trichroic the dichroic name has persisted.

 

PHYSICAL CHARACTERISTICS:

  • Color is typically blue, violet, gray, brownish or colorless.
  • Luster is vitreous.
  • Transparency crystals are transparent to translucent.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include rare prismatic crystals but is usually massive, or in compact grains embedded in metamorphic schists and gneisses. Also found as pebbles and grains in alluvial deposits.
  • Cleavage is poor in one direction.
  • Fracture is subconchoidal.
  • Hardness is 7 - 7.5
  • Specific Gravity is approximately 2.3 (light)
  • Streak is white.
  • Other Characteristics: strongly pleochroic (displays the range of colors from blue-violet to gray or colorless), index of refraction is 1.52 - 1.57.
  • Associated Minerals are almandine, corundum, andalusite, biotite and feldspars.
  • Notable Occurrences include Sri Lanka; India; Burma; Madagascar; Middlesex Co., Connecticut and the Yellowknife area of the Northwest Territories, Canada.
  • Best Field Indicators are hardness, lack of good cleavage, density, color and pleochroism. 

THE MINERAL CORDYLITE-(Ce)

 


Cordylite belongs to the rare earth carbonates, an informal and relatively rare group of minerals. Some of the other more common rare earth carbonates are ancylite, carbocernaite, synchysite, tengerite, parisite, lanthanite, ewaldite, burbankite, donnayite and bastnasite. Cordylite was first discovered at the famous mineral site of Narsarsuk, Greenland and is only found as small crystals that can be used for micromounts. Cordylite is found in carbonatites, alkaline syenites and zeolite veins. It is a rare mineral as it is known from only a few localities and then not in large amounts.

 

PHYSICAL CHARACTERISTICS:

  • Color is colorless, yellow, brownish-yellow and orange-yellow.
  • Luster is greasy to adamantine.
  • Transparency: Crystals are translucent to transparent, some specimens approach opaqueness.
  • Crystal System is hexagonal.
  • Crystal Habits include small prismatic or platy crystals, some demonstrating a hemimorphic character.
  • Cleavage is good in one direction (basal).
  • Fracture is conchoidal.
  • Hardness is typically around 4.5
  • Specific Gravity is approximately 4.0 to 4.3 (well above average)
  • Streak is white.
  • Other Characteristics: Crystals can show some striations parallel to the basal face.
  • Associated Minerals include bastnasite, calcite, aegirine, albite, quartz, ashcroftine-(Y), brookite, burbankite, carbocernaite, synchysite-(Ce), ankerite, ancylite-(Ce), mckelveyite, elpidite, narsarsukite, lorenzenite, leucosphenite and several zeolites.
  • Notable Occurrences include the type locality of Narsarsuk, Greenland. Other localities include the mines of Mont Saint-Hilaire, Quebec and Kibina, Kola Peninsula, Russia.
  • Best Field Indicators: are crystal habit, color, cleavage, density, luster and locality.

 

 

THE MINERAL CORNETITE

 

  • Chemistry: Cu3PO4(OH)3 , Copper Phosphate Hydroxide.
  • Class: Phosphates
  • Uses: mineral specimens.
  • Specimens

Cornetite is a rare secondary copper mineral that is noted for its deep blue, green-blue to green color. It is found in highly weathered, oxidation zones of copper sulfide ore bodies. It has a good deep color, nice crystal forms and an attractive sparkle, all the ingredients for a popular collection mineral.

 

PHYSICAL CHARACTERISTICS:

  • Color is dark blue, green-blue to green.
  • Luster is vitreous.
  • Transparency: Specimens are translucent.
  • Crystal System: is orthorhombic; 2/m2/m2/m
  • Crystal Habits include crystals that are short, rounded, nearly diamond-shaped prisms that are terminated by a dome with trapezohedral faces, also as tiny crystalline druzes, fibrous masses and crusts.
  • Cleavage is absent.
  • Fracture is uneven.
  • Hardness is 4.5
  • Specific Gravity is approximately 4.1 (above average for translucent minerals)
  • Streak is blue.
  • Associated Minerals are limonite, libethenite, malachite, pseudomalachite, brochantite and other secondary copper ore minerals.
  • Notable Occurrences include Shaba, Congo; Bwana Mkubwa, Zambia and Empire Nevada Mine, Yerington,Nevada.
  • Best Field Indicators are color, streak, crystal habits, associations and density.

 

THE MINERAL CORUNDUM

 

Also see variety specimens:

When someone lists the most famous gemstones such as diamond, topaz, aquamarine, emerald and garnet, corundum does not usually get mentioned. However, its two varieties are sure to be on any list of gemstones. The red variety of corundum is known as ruby and all the other colors of corundum are known as sapphire.
Corundum is the second hardest natural mineral known to science. The hardest mineral, diamond is still four times harder than corundum. The hardness of corundum can be partially attributed to the strong and short oxygen-aluminum bonds. These bonds pull the oxygen and aluminum atoms close together, making the crystal not only hard but also quite dense for a mineral made up of two relatively light elements.

 

PHYSICAL CHARACTERISTICS:

  • Color is highly variable. The color can be white or colorless, blue, red, yellow, green, brown, purple, and pink; there are also instance of color zonation.
  • Luster is vitreous to adamantine.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is trigonal; bar 3 2/m
  • Crystal Habits include sapphire's typical six-sided barrel shape that may taper into a pyramid, and ruby's hexagonal prisms and blades.
  • Cleavage is absent, although there is parting which occurs in three directions.
  • Fracture is conchoidal.
  • Hardness is 9
  • Specific Gravity is approximately 4.0+ (above average for translucent minerals)
  • Streak is white.
  • Associated Minerals include calcite, zoisite, feldspars, micas and garnets.
  • Other Characteristics: Refractive index is around 1.77; pleochroic (meaning color intensity is variable from different viewing directions); striations on parting surfaces.
  • Notable Occurrences include Burma; Sri Lanka; North Carolina and Montana, USA; many African localities; several localities in India, and Middle Eastern and Southeast Asian countries.
  • Best Field Indicators are extreme hardness, density and crystal habit.

 

THE MINERAL COVELLITE

 


Covellite is not a well known or widely distributed mineral. But its iridescent charms can captivate the admiration of anyone that looks at the indigo blue crystals. Although good crystals are rare, it is the luster and color of this mineral that make it noteworthy. The structure of covellite is somewhat analogous to the structures of the phyllosilicate minerals. In covellite some of the copper ions are at the center of sulfur tetrahedrons that are linked on their bases to form sheets. The other copper ions are combined with three sulfur ions in flat triangular groups similar to the triangular groups of the typical carbonates These triangular groups lie in a plane between the tetragonal sheets. The perfect cleavage of covellite into sheets is easily explained by this structure.

 

PHYSICAL CHARACTERISTICS:

  • Color is a deep metallic indigo blue (tarnished to purple or black) with iridescent yellow and red flashes.
  • Luster is metallic
  • Transparency crystals are opaque to translucent in very thin cleavage sheets.
  • Crystal System is hexagonal; 6/m2/m2/m
  • Crystal Habits: thin platy hexagonal crystals dominated by pinacoidal faces, usually on edge. Also massive and in small grains in sulfide ore bodies.
  • Cleavage is perfect in one direction forming thin sheets.
  • Fracture is flaky.
  • Hardness is 1.5 - 2.
  • Specific Gravity is 4.6 to 4.8
  • Streak gray to black.
  • Associated Minerals include pyrite, chalcocite, chalcopyrite, cuprite, bornite and other copper sulfides.
  • Other Characteristics: thin cleavage sheets are flexible.
  • Notable Occurances Butte, Montana; Bor, Serbia; Germany; Austria and Sardinia.
  • Best Field Indicators are crystal habit, cleavage, density, iridescence and color.

 

 

THE MINERAL CRISTOBALITE

 

  • Chemistry: SiO2, Silicon Dioxide.
  • Class: Silicate
  • Group: Quartz.
  • Uses: As an indicator of high temperature crystallization and as mineral specimens.
  • Specimens

Cristobalite is a polymorph of quartz, meaning that it is composed of the same chemistry, SiO2, but has a different structure. Both quartz and cristobalite are polymorphs with all the members of the Quartz Group which also include coesite, tridymite and stishovite.

Cristobalite is common in volcanic rocks and many microscopic crystals are easily seen in a petrographic microscope. However, larger well formed crystals are rarer and good specimens are found in the crevices and cavities (called vesicles) of the host rocks. Cristobalite's wide spread distribution in certain types of rocks would require an abundance rating of at least common, although good macroscopic crystal specimens are hard to find. Identification of cristobalite is not necessarily easy, but it is so common in volcanic rocks that crystal habit and color are usually sufficient.

Cristobalite has a higher temperature phase called beta cristobalite. Most cristobalite is believed to crystallize as beta cristobalite which has an isometric symmetry and later as the crystal cools, it easily converts to alpha cristobalite or just cristobalite. The typical crystals of beta cristobalite are octahedrons. The conversion from beta cristobalite to cristobalite is so easy that the beta cristobalite's isometric crystals are outwardly preserved in their original form. The beta cristobalite has a higher symmetry than the tetragonal symmetry of cristobalite. The interior structure is therefore not isometric anymore and thus the octahedral looking crystals are called pseudomorphs or "false shape".

The presence of cristobalite in a rock is helpful to petrologists (rock scientists) in determining the temperature of the rock at the time it crystallized. It will form from molten rock at temperatures above approximately 1470 degrees Celsius to the boiling point of silica. Pressure and water content will vary this range, but it is usually a rather good indication of the extreme temperature at which the rock crystallized. Below 1470 degrees Celsius and above 870 degrees Celsius tridymite is stable and will crystallize. Below 870 degrees Celsius, beta quartz is stable and it will crystallize. Since a molten rock goes through various temperatures as it cools all three polymorphs could be present, confusing the issue.
Cristobalite is only metastable at normal surface temperatures; meaning that, if it could, it would slowly convert to the quartz structure. But this is a slow and complicated process taking thousands of years if it happens at all. It is a slow process mostly because the transformation involves the breaking of bonds and the rearrangement of atoms. Atoms of aluminum and sodium in the structure may help the stability of cristobalite as well.

 

PHYSICAL CHARACTERISTICS:

  • Color is colorless or white.
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is tetragonal; 4 2 2 (alpha cristobalite) and isometric; 4/m bar 3 2/m (beta cristobalite).
  • Crystal Habit includes the always small (usually microscopic) and rarely well formed crystals that are pseudo-isometric, being pseudomorphs of beta cristobalite. The crystals are typically pseudo-octahedrons, some of which are twinned in a special twin called the spinel twin. The more commonly observed habit is radiating clusters and spherical aggregates.
  • Cleavage is absent.
  • Fracture is conchoidal.
  • Hardness is 6.5
  • Specific Gravity is 2.32+ (below average for translucent minerals)
  • Streak is clear.
  • Other Characteristics: Refractive index is approximately 1.48
  • Associated Minerals include tridymite, sanadine, hornblende, beta quartz, olivine, pseudobrookite and augite.
  • Notable Occurrences include Cerro San Cristobal, Pachuca, Mexico (from where it gets its name); San Juan Mountains and Yellowstone National Park, both in Colorado and Mt. Lassen, California, USA and Italy.
  • Best Field Indicators are crystal habit, environment of formation (mostly in the crevices of volcanic rocks), color and index of refraction.

 

 

THE MINERAL CROCOITE

 

  • Chemistry: PbCrO4 , Lead Chromate
  • Class: Sulfates
  • Subclass: Chromates
  • Uses: Only as mineral specimens and as a minor ore of chromium.
  • Specimens

Crocoite is a rather unusual lead mineral and can be a beautiful and colorful specimen. Crocoite provides a nice color to the mineral kingdom and is well known for its distinctive orange-red color. Its main source of quality specimens comes from the Dundas District of Tasmania, Australia. The crystals there are usually long thin prisms. However, large crystals from this locality have been scarce in the past thirty years. Most specimens do not have any crystals over 5 cm long. Crocoite's high density and luster are the result of its lead content. Some crocoite aggregates are composed of bars and splinters, of differing sizes, going in a dozen different directions and produces a certain character to these specimens that is distinctive of crocoite. Crocoite is also one of the very few chromate minerals. Beautiful specimens that show off crocoite's unique color, high luster and unusual character are a prized addition to anyones collection.

 

 

PHYSICAL CHARACTERISTICS:

  • Color is bright orange-red to yellowish-red.
  • Luster is adamantine to greasy.
  • Transparency: Crystals are translucent to transparent.
  • Crystal System is monoclinic; 2/m
  • Crystal Habits include prismatic crystals somewhat square in cross-sections, often striated lengthwise. Terminations are usually poorly developed and appear uneven or pitted. Also, granular and columnar.
  • Cleavage is distinct in two directions lengthwise, prismatic.
  • Fracture is conchoidal and uneven.
  • Hardness is 2.5 - 3.
  • Specific Gravity is approximately 6.0+ (very heavy for translucent minerals)
  • Streak is orange-yellow.
  • Other Characteristics: Index of refraction is a very high 2.36
  • Associated Minerals are wulfenite, pyromorphite, cerussite, limonite and vanadanite.
  • Notable Occurrences include Dundas District, Tasmania, Australia; Ural Mountains, Russia and Inyo and Riverside Counties in California, USA.
  • Best Field Indicators are crystal habit, locality, density, high luster and color.

 

 

THE MINERAL CRYOLITE

 

  • Chemistry: Na3AlF6, Sodium Aluminum Fluoride
  • Class: Halides
  • Uses: as a aid to aluminum processing and other industrial uses and as mineral specimens.
  • Specimens

Cryolite is an uncommon mineral of very limited natural distribution. Mostly considered a one locallity mineral, for although there are a few other minor locallities, it was only found in large quantities on the west coast of Greenland.
It was used as a solvent of the aluminum rich ore, bauxite, which is a combination of aluminum oxides such as gibbsite, boehmite and diaspore. It is very difficult to remove atoms of aluminum from atoms of oxygen which is necessary in order to produce aluminum metal. Cryolite made an excellent flux to make the process less expensive. Now it is too rare to be used for this purpose and sodium aluminum fluoride is produced artificially to fill the void.
A curious note about cryolite is the fact that it has a low index of refraction close to that of water. This means that if emersed in water, a perfectly clear colorless crystal of cryolite or powdered cryolite will essentially disappear. Even a specimen of cloudy cryolite will become more transparent and its edges will be less distinct, an effect similar to ice in water except that the ice floats.

 

PHYSICAL CHARACTERISTICS:

  • Color is clear or white to yellowish, but can also be black or purple.
  • Luster is vitreous.
  • Transparency crystals are transparent to translucent.
  • Crystal System is monoclinic; 2/m
  • Crystal Habits are usually massive and as pseudo-cubic crystals, some with psuedo-octahedral truncations.
  • Cleavage is absent, but three parting directions produce what looks like a psuedo-cubic cleavage.
  • Fracture is uneven.
  • Hardness is 2.5 - 3
  • Specific Gravity is 2.95 (average)
  • Streak is white.
  • Other Characteristics: index of refraction is 1.338 which is close to the index of refraction of water. As a consequence, clear cryolite crystals or powdered cryolite will nearly disappear in water. Also there is no salty taste which is helpful in distinguishing cryolite from the mineral halite.
  • Associated Minerals include siderite, quartz, topaz, fluorite, chalcopyrite, galena, cassiterite, molybdenite, columbite and wolframite.
  • Notable Occurances include Ivigtut area of Greenland and also at the foot of Pikes Peak at Creede, Colorado, USA, Mont Saint-Hilaire and Francon Quarry, Montreal, Quebec, Canada and at Miask, Russia.
  • Best Field Indicators are lack of salty taste, density, index of refraction, locallity and crystal habit.

 

 

THE MINERAL CUBANITE

 

  • Chemistry: CuFe2S3, Copper Iron Sulfide.
  • Class: Sulfides
  • Uses: A very minor ore of copper and as mineral specimens.
  • Specimens

Cubanite (also known as "chalmersite") is a rare copper mineral that does not contribute much to the supply of copper. It would not even be considered an ore of copper except that it is often interbedded with other ores of copper and so it does contribute some copper when these other ores, such as chalcopyrite, are processed. Cubanite is also associated with gold in some gold mines.

It is far more desired as a mineral specimen. Cubanite has a bright metallic luster and a brassy golden color that is really striking. It commonly forms twins that are seen as either sharply pointed chevrons or as cyclic twins of six rayed "stars" or "flowers". Cubanite is named after Cuba, the country of its type locality.

 

PHYSICAL CHARACTERISTICS:

  • Color is a brassy golden yellow.
  • Luster is metallic.
  • Transparency: Crystals are opaque.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include elongated prismatic to tabular crystals. Crystals sometimes twinned into chevrons and six rayed cyclic "stars" or "flowers". Also lamellar, rarely massive.
  • Cleavage is rather poor in one direction.
  • Fracture is conchoidal.
  • Hardness is 3.5 - 4
  • Specific Gravity is approximately 4.1 (average for metallic minerals)
  • Streak is black.
  • Other Characteristics: Deep longitudinal striations on most crystal faces.
  • Associated Minerals are chalcopyrite, quartz, gold, siderite, calcite, pyrite, pyrrhotite and several copper sulfides.
  • Notable Occurrences include Barracanao, Cuba; Morro Velho gold mine, Minas Gerais, Brazil; Harz Mnts, Germany and the Henderson Mine, Chibougamau, Quebec, Canada.
  • Best Field Indicators are crystal habit especially its twins, color, luster and occurrence.

 

THE MINERAL CUMENGITE

 

  • Chemistry: Pb21Cu20Cl42(OH)40, Lead Copper Chloride Hydroxide.
  • Class: Halides
  • Uses: A very minor ore of lead and copper and as mineral specimens.
  • Specimens

Cumengite (also spelled cumengeite) is a rare mineral and of great interest to collectors of rare halides. It shares a close relationship with another rare halide, boleite. Boleite and cumengite both come from the same type locality at Boleo, Baja California, Mexico; both resulted from the oxidation of igneous copper ore bodies; both have similar chemistries, although cumengite lacks silver; both have an attractive indigo blue color and both have interesting crystal forms. But all that is not the reason for the close relationship. Cumengite and boleite have about as close a relationship as two minerals can have since cumengite actually grows on the cube faces of boleite crystals. Other minerals grow randomly on other minerals, but in this case the two structures are crystallographically oriented as if the cumengite's structure found enough of a similarity of boleite's structure to its own, that it could continue the growth where boleite left off and "finish" the crystal. This relationship is called an epitaxial overgrowth and is found on other minerals but it is cumengite's example that is most amazing. On a fully developed specimen, each of the six faces of the boleite's cube are capped with a four sided pyramid of cumengite. The resulting aggregate is a true mineralogical curiosity, a six pointed, 3 dimensional, indigo blue star. Unfortunately, there are not many complete specimens in existence and even partial stars are valuable.

Cumengite is named after Eduoard Cumenge, a French mining engineer who is believed to be the first to collect specimens of cumengite and boleite. Cumengite contains hydroxides in its formula and belongs to a division of the Halides Class called the Oxyhalides and Hydroxyhalides and some other members include bideauxite, chloroxiphite, kelyanite, blixite, pseudoboleite, botallackite, laurionite, paralaurionite, mendipite, fiedlerite, pinchite, diaboleite, penfieldite, yedlinite, atacamite, koenenite, zirklerite and paratacamite. The beautiful color, unusual chemistry, extremely interesting crystal habit and rarity make cumengite a most desirable collection piece.

 

PHYSICAL CHARACTERISTICS:

  • Color is indigo blue with violet tints.
  • Luster is vitreous.
  • Transparency: Crystals are usually transparent to translucent on thin edges.
  • Crystal System is tetragonal
  • Crystal Habits include pseudo-octahedral crystals, but more commonly found as epitaxial overgrowths on boleite. Each of the six faces of the boleite's cube can be capped with a four sided pyramid of cumengite. The result is a six pointed, 3 dimensional, star-shaped aggregate.
  • Cleavage is numerous and includes four good to distinct directions and one poor direction (basal).
  • Fracture is uneven and brittle.
  • Hardness is 2.5
  • Specific Gravity is 4.6 (rather heavy for translucent minerals)
  • Streak is blue.
  • Associated Minerals include pseudoboleite and especially boleite.
  • Notable Occurrence is limited to the type locality of Boleo, Santa Rosalia, Baja California, Mexico.
  • Best Field Indicators are crystals habit, color, density, associations and locality.

 

 

THE MINERAL CUMMINGTONITE

 

  • Chemistry: (Mg, Fe)7Si8O22(OH)2 , Magnesium Iron Silicate Hydroxide.
  • Class: Silicates
  • Subclass: Inosilicates
  • Group: Amphibole
  • Uses: Are limited to some asbestos uses and as mineral specimens.
  • Specimens

Cummingtonite is the name of a series as well as the name of a mineral. The mineral cummingtonite, is basically the middle member of the Cummingtonite Series, which include the minerals grunerite and magnesiocummingtonite. All three minerals' formulae are essentially the same: (Mg, Fe)7Si8O22(OH)2. However the percentage of magnesium to iron varies in the series and determines the mineral whereas, little else does. In grunerite, the iron rich member, the ratio of Mg/(Mg +Fe) equals 0.00 to 0.29; but in magnesiocummingtonite, as the name implies it is magnesium rich, the ratio equals 0.70 to 1.00. Cummingtonite by default has a ratio of 0.30 to 0.69, the majority of the middle and as can be expected is the most common member of the series.

Cummingtonite shares its formula with another mineral called anthophyllite. Cummingtonite and anthophyllite are polymorphs, a situation where two minerals share the same chemistry but have different structures (poly=many, morphs=shapes). Diamond and graphite are the most famous examples of polymorphism. In the case of anthophyllite and cummingtonite; anthophyllite is orthorhombic and cummingtonite is monoclinic. The two minerals can have similar distinctive brown colors and are hard to differentiate from each other, although cummingtonite is typically darker and slightly denser. Despite their distinctive brown color, the two are often indistinguishable from other amphiboles without optical or X-ray tests.

Cummingtonite is a common component of some regional metamorphic rocks. If more intense metamorphism were to occur the minerals hypersthene, enstatite or olivine are produced at the expense of cummingtonite. Retrograde metamorphism can conversely restore cummingtonite as well as other iron-magnesium amphiboles.

One form of cummingtonite (a variety called "amosite") is asbestos-form and can be used as asbestos. Asbestos has many industrial uses despite some health risks and is made from different minerals, all with a fibrous habit. Serpentine and tremolite asbestos are considered the better varieties due to their greater flexibility and tensile strength, but cummingtonite asbestos has its uses and is being mined for this reason in South Africa.

 

PHYSICAL CHARACTERISTICS:

  • Color is a dark grayish or greenish-brown and dark green.
  • Luster is silky to vitreous.
  • Transparency: Crystals are translucent to opaque.
  • Crystal System is monoclinic; 2/m.
  • Crystal Habits include fibrous, lamellar and radiating masses. Twinning is common and is either simple or lamellar.
  • Cleavage: is good in two directions at 56 and 124 degree angles.
  • Fracture is splintery.
  • Hardness is 5 - 6.
  • Specific Gravity is approximately 3.1 - 3.6 (average to slightly above average).
  • Streak is white.
  • Other Characteristics: Non-pleochroic.
  • Associated Minerals are hematite, hornblende, actinolite and anthophyllite.
  • Notable Occurrences include Cummington (hence the name), Hampshire County, Massachusetts; Homestake gold mine, Lawrence County, South Dakota and La Paz County, Arizona, USA; Scotland; South Africa and Sweden.
  • Best Field Indicators are crystal habit, fracture, cleavage, color, density and hardness.

 

 

THE MINERAL CUPRITE

 


Cuprite has been a major ore of copper and is still mined in many places around the world. Of all the copper ores except for native copper, cuprite gives the greatest yield of copper per molecule since there is only one oxygen atom to every two copper atoms. As a mineral specimen, cuprite shows fine examples of well-developed cubic crystal forms. Cuprite's dark crystals show internal reflections of the true deep red inside the almost black crystal. Other varieties, such as chalcotrichite, show tufts of needle-like crystals that have a beautiful red color and a special sparkle that make them popular display cabinet specimens.

 

PHYSICAL CHARACTERISTICS:

  • Color is red to a deep red that can appear almost black.
  • Luster is adamantine or submetallic to dull or earthy if massive.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is isometric; once thought to be 4 3 2 but now believed to belong to 4/m bar 3 2/m.
  • Crystal Habits include the cube, octahedron, dodecahedron, and combinations of these forms. Some display faces of the obscure gyroid form. A variety known as Chalcotrichite forms long needle-like crystals or fuzzy crusts. also massive.
  • Cleavage is fair in four directions forming octahedrons.
  • Fracture is conchoidal.
  • Hardness is 3.5-4
  • Specific Gravity is approximately 6.0 (very heavy for translucent minerals)
  • Streak is brick red.
  • Associated Minerals are limonite, copper, chrysocolla, malachite and other secondary copper minerals.
  • Other Characteristics: Forms a surface film with long exposure to strong light. Crystals of cuprite are sometimes altered or partially altered to malachite and rarely copper.
  • Notable Occurrences include Arizona, USA; Africa; Australia; Chile and several localities in Europe.
  • Best Field Indicators are color, crystal form and softness.

 

 

 

 

THE MINERAL CUPROADAMITE

 


Cuproadamite is not always thought of as a separate mineral from its close cousin adamite. However it is increasingly being sold and distributed as cuproadamite, although it has yet to be officially acknowledged as a separate mineral. It contains an appreciable amount of copper and this usually colors the crystals a reddish purple to amethyst purple. Cuproadamite is an intermediate "mineral" between adamite - Zn2AsO4(OH) and olivenite - Cu2AsO4(OH).

Unfortunately for collectors who love fluorescent minerals(adamite is one of the best fluorescing minerals in the world), cuproadamite does not fluoresce at all. The copper acts as a "poison" for the fluorescence, making for a fairly reliable test to distinguish cuproadamite from adamite. The test is not foolproof however, as some adamites that contain little or no copper do not fluoresce either. Nearly all properties of cuproadamite are identical to adamite except typical color, density and fluorescence.

PHYSICAL CHARACTERISTICS:

  • Color is typically reddish purple, but can be purple, red or even green.
  • Luster is adamantine.
  • Transparency crystals are transparent to translucent.
  • Crystal System is orthrombic; 2/m 2/m 2/m
  • Crystal Habits include diamond-shaped, wedge-like prisms sometimes modified with minor prismatic faces and terminated by a double triangle. Mostly in druses and radiating clusters that can form wheel and "wheat-sheath" shapes. Rarely in a perfectly smooth botryoidal habit like smithsonite, but commonly found with well-formed crystal terminations that sparkle on the top of the "sub-botryoidal" surface.
  • Cleavage is perfect in one direction.
  • Fracture is conchoidal.
  • Hardness is 3.5.
  • Specific Gravity is approximately 4.6 (heavy for translucent minerals and slightly heavier than adamite)
  • Streak is white.
  • Other Characteristics: does not fluoresces like its cousin adamite.
  • Associated Minerals are adamite, limonite, conichalcite, smithsonite, aragonite, calcite, and other oxidation zone minerals.
  • Notable Occurances include the famous mines at Mapimi, Mexico; also Greece and other sites that contain adamite and copper minerals.
  • Best Field Indicators are color, density, non-fluorescences, associations and crystal habits.

 

 

 

 

THE MINERAL CUPROSKLODOWSKITE

 

  • Chemistry: Cu(UO2)2Si2O7 - 6H2O, Hydrated Copper Uranyl Silicate.
  • Class: Silicates
  • Subclass: Nesosilicates
  • Uses: mineral specimen and very minor ore of uranium
  • Specimens

Cuprosklodowskite is a rare uranium mineral that formed from the oxidation of copper and uranium bearing minerals. Found in good crystals only at one mine at the world famous copper and uranium mines of Shaba, Zaire. The Musonoi Mine produces the worlds supply of the finest cuprosklodowskite specimens. Sklodowskite and uranophane are two closely related minerals that have similar chemistry, structure and crystal habits. Cuprosklodowskite's bright green velvety tufts of hair-like crystals are very attractive and make an impressive mineral specimen. With its rarity and beauty, cuprosklodowskite is much sought after by rare mineral collectors. Remember, this is a radioactive mineral and should be stored away from other minerals that are affected by radioactivity and human exposure should be limited.

 

PHYSICAL CHARACTERISTICS:

  • Color is dark green.
  • Luster is vitreous to silky.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System: Triclinic; bar 1
  • Crystal Habits are typically fibrous tufts and crusts. Also acicular crystals in radial aggregates.
  • Cleavage: perfect in one direction.
  • Hardness is 4.
  • Specific Gravity is approximately 3.8 (above average for translucent minerals)
  • Streak is green.
  • Associated Minerals are uraninite, dioptase, sklodowskite, Uranophane and brochanitite.
  • Other Characteristics: Radioactive and fluorescent.
  • Notable Occurrences include Musonoi Mine, Shaba, Zaire; Amelal, Morocco and San Juan Co., Utah.
  • Best Field Indicators are crystal habit, color, locality, radioactivity and fluorescence.

 

 

 

 

THE MINERAL CYANOTRICHITE

 

  • Chemistry: Cu4Al2SO4(OH)12 - 2H2O, Hydrated Copper Aluminum Sulfate Hydroxide.
  • Class: Sulfates
  • Uses: Only as mineral specimens.
  • Specimens

Cyanotrichite is a wonderfully colored mineral. Its bright azure to sky blue color is very impressive. Cyanotrichite typically forms acicular or hair like crystals aggregated into radial clusters, tufts and sprays. The color is very impressive for such tiny crystals. It is an aptly named mineral since cyano and trich are derived from the Greek for blue and hair, respectively. It is formed from the oxidation of copper ore minerals along with other oxidation zone minerals.

 

PHYSICAL CHARACTERISTICS:

  • Color is bright azure blue to sky blue.
  • Luster is vitreous to silky.
  • Transparency crystals are mostly translucent.
  • Crystal System is orthorhombic.
  • Crystal Habits include acicular to fibrous crystals aggregated into coatings, tufts, radial clusters and sprays as well as small tabular crystals.
  • Cleavage is absent.
  • Fracture is uneven.
  • Hardness is 3 - 4.5
  • Specific Gravity is approximately 3.7 - 3.9+ (above average for translucent minerals)
  • Streak is blue.
  • Associated Minerals are brochantite, smithsonite, malachite and azurite.
  • Notable Occurrences include Laurium, Greece; Leadhills, Scotland; Russia; South Africa; Arizona, Nevada and Utah, USA and France.
  • Best Field Indicators are crystal habit, associations and color.

 

 

THE MINERAL CYLINDRITE

 

  • Chemistry: FePb3Sn4Sb2S14, Iron Lead Tin Antimony Sulfide
  • Class: Sulfides
  • Subclass: Sulfosalts
  • Uses: Mineral specimens and as a very minor ore of lead and tin.
  • Specimens

Cylindrite is a most unusual sulfide mineral. It has an extremely unique crystal habit- one so unique that it pretty much corners the market on this crystal habit. Cylindrite as its name implies, forms cylindrical crystals. The crystals are actually coiled sheets that give the appearance of having been rolled into tubes or cylinders. Under pressure the sheets, often described as leaves or shells, become uncoiled. The only crystal habit similar to this is at a microscopic level and occurs with chlorite and serpentine and results in tubes resembling hairs. Cylindrite's tubes are visible to the eye, but may require a hand lense or loop to see the fine detail. With this unusual crystal habit, cylindrite is a must have for someone who likes one-of-a-kind forms.

 

 

PHYSICAL CHARACTERISTICS:

  • Color is iron black to gray.
  • Luster is metallic.
  • Transparency: Crystals are opaque.
  • Crystal System is trigonal, but is in dispute.
  • Crystal Habit is extremely unique. Crystals form small wrapped cylinders (hense the name) that look like tubes or rolls of metallic cloth. Also found massive.
  • Cleavage: None.
  • Fracture: Conchoidal to uneven.
  • Hardness is 2.5
  • Specific Gravity is 5.4 - 5.5 (somewhat heavier than average for metallic minerals)
  • Streak is black.
  • Other Characteristics: Under pressure, cylinders will separate into curved shells or leaves.
  • Associated Minerals include pyrite, sphalerite, cassiterite, teallite and franckeite.
  • Notable Occurrences are limited to Mina Santa Cruz, Poopo, Oruro, Bolivia and a few other tin sulfide deposits.
  • Best Field Indicators include the very unusual crystal habit as well as the locality, softness, color and luster.
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