Tuesday, August 23, 2011

Mineral R


THE MINERAL RAITE

 


Raite is a rare and beautiful mineral. It was named in 1973 to honor the international scientific expedition of the ship "Ra II" which was built of papyrus. The ship was captained by Thor Heyerdahl, a Norwegian explorer and scientist who was determined to prove the sea worthiness of reed boats. The Ra II was successfully sailed from Safi, Morocco to Barbados in 1970.

Raite is a bit of an oddball mineral in that its structure is hard to classify. It is classified as a phyllosilicate in the Dana classification scheme and as a inosilicate in the Strunz classification scheme. The structure of raite is composed of linked chains of silicates, four chains across. Dana considers this a sheet structure and therefore a phyllosilicate, while Strunz considers this to still be a chain structure and therefore an inosilicate.

Raite is another rare and beautiful agpaitic mineral. Agpaitic minerals are those found in unusual igneous intrusive rocks that contain alkali metals and high concentrations of unusual metals such as titanium and zirconium. These rocks are called agpaites and there are only a few localities around the world that are identified as agpaites. At two of these, raite is found; Mount Saint Hilaire, Quebec, Canada and Mt. Lovozero Massif, Kola Peninsula, Russia. At both sites, raite forms beautiful acicular crystals arranged in sprays, fans, spherulites, rosettes and as crusts. The color is golden-brown to red or even violet with a silky luster. It is associated with other rare minerals and although hard to find, it is certainly a cool mineral to have in a collection.

 

PHYSICAL CHARACTERISTICS:

  • Color is golden-brown to red or even violet.
  • Luster is silky to vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is orthorhombic; 2 2 2
  • Crystal Habits include acicular crystals and aggregates are clustered into sprays, fans, spherulites, rosettes and as crusts.
  • Cleavage is perfect, but rarely seen.
  • Hardness is 3.
  • Specific Gravity is 2.4
  • Streak is yellow.
  • Associated Minerals are aegirine, epididymite, analcime, albite, villiaumite, natrolite, zorite, eudialyte, sodalite, sphalerite, ancylite, nenadkevichite, lovozerite, mangan-neptunite, penkvilksite, serandite and other rare minerals.
  • Notable Occurrences include the type locality of Yubileinaya pegmatite, Karnasurt, Mt. Lovozero Massif, Kola Peninsula, Russia and the famous mineral site of Mount Saint Hilaire, Quebec, Canada.
  • Best Field Indicators are crystal habit, locality, associations and color.

 

 

 

 

 

 

THE MINERAL RAMMELSBERGITE

 


Rammelsbergite is a difficult mineral to distinguish from other nickel sulfides and related arsenides. Its unusually high hardness and silvery color helps, but mostly it is indistinguishable from many of them by ordinary methods. It had been reported to have been found at Franklin, New Jersey, but this may have been a misidentification with the mineral gersdorffite, a similar looking nickel arsenic sulfide.

Rammelsbergite is a rare mineral, but is found with other arsenides and thus it is included with them when mined for nickel and/or arsenic. It is a member of the Lollingite Group. The namesake of the group, lollingite is closely related, but has more iron than nickel in its chemistry. Another closely related mineral is saffloriite, which has more cobalt than nickel. The three minerals share the same basic structure and just differ by chemistry. The lollingite group is sometimes placed in the larger Marcasite Group.

Rammelsbergite lends it name to its dimorphic cousin, pararammelsbergite. A dimorph is a set of two minerals that share the same chemistry, but have different structures. Pararammelsbergite has monoclinic symmetry, while rammelsbergite's is orthorhombic, (the prefix para just means "similar to...").

 

PHYSICAL CHARACTERISTICS:

  • Color is silvery white, almost reddish (tarnishes to yellow or pink).
  • Luster is metallic.
  • Transparency: Crystals are opaque.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include rare tabular to stubby crystals, sometimes in cock's comb habit. More commonly found fibrous (radially), massive and granular.
  • Cleavage is absent.
  • Fracture: Uneven.
  • Hardness is 5.5 - 6
  • Specific Gravity is approximately 6.9 - 7.1 (well above average for metallic minerals)
  • Streak is a gray.
  • Associated Minerals include niccolite, gersdorffite, quartz, annabergite, pyrite, lollingite, chloanthite, arsenic, cobaltite, arsenopyrite and silver.
  • Notable Occurrences include the Sainte-Marie-Aux-Mines district, France; Great Bear Lake and the Frontier Mine, Cobalt, Ontario, Canada; Kongsberg, Norway; Binntal Switzerland; Lolling, Austria; Bou Azzer, Morocco; Batopilas, Chihuahua, Mexico; Keweenaw, Michigan and the type locality of Schneeburg, Harz Mountains, Germany.
  • Best Field Indicators are crystal habits, color (tarnish), associations, streak, hardness and density.



  

THE MINERAL RAMSDELLITE

 


Ramsdellite is a rather uncommon mineral to be seen in mineral markets. Partly because of its rarity, partly because of its general lack of good crystals and partly because of its difficulty in being identified. Ramsdellite is polymorphous (meaning many shapes) with the relatively common mineral pyrolusite. The two minerals have the same chemistry, but different structures. Pyrolusite is tetragonal and ramsdellite is orthorhombic. A third mineral, akhtenskite, is much more rare than these two and is also a polymorph being hexagonal. The three minerals are thus referred to as trimorphs.

Ramsdellite is an oxidation product of weathered manganese minerals, such as manganite. Ramsdellite is often a minor constituent of "Wad". The mining term "wad" is used to indicate massive ores that are a mixture of several manganese oxides such as pyrolusite, psilomelane, ramsdellite and others that are difficult to distinguish. Manganese is a strategically valuable metal since it is an essential ingredient in steel and other alloys.

 

PHYSICAL CHARACTERISTICS:

  • Color is black to gray.
  • Luster is metallic to dull.
  • Transparency: Crystals are opaque, translucent in only thin splinters.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habit is typically massive and granular. Crystals are uncommon and tabular.
  • Cleavage is good , but rarely seen except in rare large crystals.
  • Fracture is conchoidal to uneven.
  • Hardness is approximately 3, but is variable.
  • Specific Gravity is 4.4 - 4.8 (average for metallic minerals)
  • Streak is black.
  • Associated Minerals are limonite, hematite, quartz, manganite, psilomelane, pyrolusite and other manganese and iron oxide minerals.
  • Notable Occurrences include nice specimens from Germany; former Czechoslovakia; Lake Valley, New Mexico, Minnesota, California and Montana, USA.
  • Best Field Indicators are habits, luster, softness, color and streak.





   

THE MINERAL REALGAR

 

  • Chemistry: AsS, Arsenic Sulfide
  • Class: Sulfides and Sulfosalts
  • Uses: A major ore of arsenic, formerly used for pigments, firework coloring agent and as mineral specimens.
  • Specimens

Realgar is an oddball among the sulfides. It is one of only a few sulfides that are not metallic or opaque or blandly colored. Its structure is analogous to that of sulfur and resembles sulfur in most respects except for color (the name "ruby sulfur" has been applied to realgar). Sulfur has a structure composed of 8 sulfur atoms linked in a ring. Realgar's structure alternates between sulfur atoms and arsenic atoms producing rings of As4S4. The arsenic atoms affect the structure altering it from sulfur's orthorhombic symmetry to realgar's monoclinic symmetry.
Realgar occurs in hydrothermal veins with valuable metal sulfide ores and its bright red color can be an aid to prospectors. It also can be found in hot spring deposits and as a volcanic sublimate product (crystallizing from vapors). Realgar gets its name from the Arabic words for "powder of the mine" (rahj al ghar). Realgar is famous for some wonderfully beautiful specimens. Some specimens can have a deep ruby red color with an amazing clarity and a high luster. The color of realgar is truly something to appreciate and cherish. But realgar's beauty is sometimes fleeting.

It is an unstable mineral and will alter to a different mineral, pararealgar and eventually to a powder. This process takes time and is accelerated by exposure to light. Specimens should be stored in dark, enclosed containers, and only exposed to light for the brief enjoyment of its owner and friends. This sounds extreme, but wonderfully beautiful realgar specimens are worth preserving for as long as possible. If you are wondering how quickly the deterioration occurs, the answer is immediately, but fortunately very slowly. Ancient Chinese carvings of realgar are still in existence, but badly affected by the deterioration. The deterioration of realgar was thought to produce the closely related yellow orpiment, but this was recently proven to be false and the deterioration product is in fact yellow-orange pararealgar. In old paintings and manuscripts, realgar was a common pigment for paints and dyes. Many of these paintings now have a yellow or orange hue where once the color must have been an original red.

 

PHYSICAL CHARACTERISTICS:

  • Color is orange to red.
  • Luster is resinous, adamantine to sub-metallic.
  • Transparency: Crystals are translucent to transparent.
  • Crystal System: Monoclinic; 2/m.
  • Crystal Habits: include prismatic striated crystals with a rounded diamond-like cross-section. They are terminated by a wedge-like dome. Also found as grains, crusts and earthy masses.
  • Cleavage is good in one direction.
  • Fracture is subconchoidal.
  • Hardness is 1.5 - 2
  • Specific Gravity is 3.5 - 3.6
  • Streak is orange to orange-yellow.
  • Other Characteristics: Realgar is unstable in light; specimens should be stored in complete darkness, rarely some specimens fluoresce under UV light and crystals are pleochroic between dark red and orange red.
  • Associated Minerals almost always include orpiment, also calcite, stibnite and other metal sulfide ores.
  • Notable Occurrences include most importantly Hunan Province, China; but also Switzerland; Japan; Macedonia; Mercur, Utah, USA; Romania and many other localities.
  • Best Field Indicators are of course color as well as crystal habit, association with orpiment, softness and luster.

 

 

 

 

 

THE MINERAL RHABDOPHANE

 

  • Chemistry: (Ce, La, Nd)PO4 - H2O, Hydrated Cerium Lanthanum Neodymium Phosphate.
  • Class: Phosphates
  • Group: Rhabdophane
  • Uses: As a minor ore of cerium and as mineral specimens.
  • Specimens

Rhabdophane is one of several rare earth phosphate minerals. Xenotime - (Y), monazite, churchite - (Y), florencite and belovite - (Ce) are a few of the more common ones. Although not very common, rhabdophane is common enough to be considered an ore of cerium. Rhabdophane is a mineral that forms from the alteration of rare earth igneous minerals and as a primary mineral in carbonatites and in a few rare hydrothermal veins. Its most noticeable feature is it greasy luster and botryoidal habit. Rhabdophane was named for its spectral signature which reveals the tell-tail spectral lines of its rare earth elements. Rhabdophane is basically Greek for "rods appearing".

Rhabdophane is actually a collection of three officially recognized minerals that are distinguished by their percentages of rare earth elements. Each is named for the rare earth element that composes the highest percentage of rare earth elements in that particular mineral. The three minerals are Rhabdophane - (Ce), Rhabdophane - (La), Rhabdophane - (Nd) All are very similar and difficult to distinguish. Most rhabdophane specimens are rhabdophane - (Ce) and this is most likely the mineral that is referred to when specimens are labeled simply as "rhabdophane".

Rhabdophane lends its name to a small group of phosphates. All members of the Rhabdophane Group are hexagonal or pseudo-hexagonal and have a general formula of (X)PO4 - 1-2H2O. The X can be either calcium, cerium, lead, lanthanum, neodymium, thorium, iron and uranium. Some sulfate ions, (SO4), can replace a portion of the phosphate ions, (PO4).

These are the members of the Rhabdophane Group:
  • Brockite (Hydrated Calcium Thorium Cerium Phosphate)
  • Grayite (Hydrated Thorium Lead Calcium Phosphate)
  • Ningyoite (Hydrated Uranium Calcium Cerium Phosphate)
  • Rhabdophane - (Ce) (Hydrated Cerium Lanthanum Phosphate)
  • Rhabdophane - (La) (Hydrated Lanthanum Cerium Phosphate)
  • Rhabdophane - (Nd) (Hydrated Neodymium Cerium Lanthanum Phosphate)
  • Tristramite (Hydrated Calcium Uranium Iron Phosphate Sulfate)

 

PHYSICAL CHARACTERISTICS OF RHABDOPHANE:

  • Color is white, yellowish, pink to reddish brown.
  • Luster is greasy to dull.
  • Transparency: Specimens are translucent.
  • Crystal System is hexagonal; 6 2 2.
  • Crystal Habits include tiny hexagonal prisms but more commonly found as encrusting, massive, botryoidal and stalactitic formations.
  • Cleavage is absent.
  • Fracture is uneven.
  • Hardness is 3.5 - 4.
  • Specific Gravity is approximately 4.0 (above average for translucent minerals)
  • Streak is white.
  • Associated Minerals include limonite, serandite, amphiboles, natrolite, aegirine, astrophyllite, albite, calcite, biotite, rhodochrosite and rare earth granitic minerals.
  • Notable Occurrences include Majuba Hill, Pershing County, Nevada and Salisbury, Litchfield County, Connecticut, USA; Gakaia, Burundi: Fowey Consols, Cornwall, England; Grube Clara, Oberwolfach, Germany; Mt Weld, Western Australia; Kola Peninsula, Russia and Mont Saint-Hilaire, Quebec, Canada.
  • Best Field Indicators are crystal habit, color, luster and locality.



 

    

THE MINERAL RHENIITE

 


Rheniite is a very rare and a very new mineral on the mineral market. It is so new that it is not yet listed in mineral indexes. It is found at the Kudriary Volcano, Iturup Island, Russia and is the only known rhenium mineral.

Rhenium has been found as a trace element in columbite, molybdenite, gadolinite and some platinum ores. Molybdenite, MoS2, is the only real ore of rhenium, a useful and expensive metal. The rhenium is only a trace element in the molybdenite but is found in enough concentration, up to 0.2%, and enough molybdenite is processed for molybdenium that over 100 tons of rhenium are known to exist in the world.

 

 

PHYSICAL CHARACTERISTICS:

  • Color is a bright metallic silver white.
  • Luster is metallic.
  • Transparency crystals are opaque.
  • Crystal Habits include tiny thin, platy crystals and disseminated grains and masses.
  • Specific Gravity is 7.5 measured (above average for metallic minerals)
  • Streak is black.
  • Notable Occurrence: Kudriary Volcano, Iturup Island, Russia.
  • Best Field Indicators are crystal habit, locality and color.




   

THE MINERAL RHODIZITE

 

  • Chemistry: (K, Cs)Be4Al4(B, Be)12O28, Potassium Cesium Beryllium Aluminum Borate.
  • Class: Carbonates
  • Subclass: Borates
  • Uses: As mineral specimens and sometimes cut as a gemstone.
  • Specimens

Rhodizite is a rare potassium cesium beryllium aluminum borate mineral. Just its chemistry gives away its rarity. Specimens come from only a few areas: a couple of sites in the Ural Mountains, and a few sites in Madagascar. Rhodizite is remarkable for not only its chemistry but its bright adamantine luster and high degree of hardness. Both these properties lend themselves well to the fashioning of a gemstone. Rhodizite is too rare and generally lacks good color to be used often as a gemstone however.

Do not confuse rhodizite for other similar sounding minerals such as the silicate mineral rhodonite, the carbonate mineral rhodochrosite or the silicate mineral rhodesite. They may sound alike but they are actually very different!

 

PHYSICAL CHARACTERISTICS:

  • Color is colorless to white or gray and also with pale tints of yellow.
  • Luster is vitreous to adamantine or silky.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is isometric.
  • Crystal Habits include dodecahedral crystals and embedded grains.
  • Cleavage is absent.
  • Hardness is 8
  • Specific Gravity is approximately 3.3 - 3.4 (slightly above average for translucent minerals)
  • Streak is white.
  • Other Characteristics: Index of refraction is 1.69 .
  • Associated Minerals include the red tourmaline elbaite.
  • Notable Occurrences include Antandrokomby, the Sahatany Valley of the Antisarabe area and Manjakandriana, Madagascar and Sarapulsk and Schaitansk, Mursinsk in the Urals Mountains of Russia.



















THE MINERAL
RHODOCHROSITE

  • Chemistry: MnCO3, Manganese Carbonate
  • Class: Carbonates
  • Group: Calcite Group
  • Uses: As a minor ore of manganese, an ornamental and semi-precious gemstone and as mineral specimens.
  • See our natural rhodochrosite mineral Specimens
  • For rhodochrosite jewelry, see our Affiliates

Rhodochrosite (whose name means rose-colored) is a very attractive mineral with an absolutely one-of-a-kind, beautiful color. Although it can be an ore of manganese, it is its ornamental and display specimen qualities that make it a very popular mineral. The color of a single crystal can just astound the observer with its vivid pink-rose color that seems to be transmitted out of the crystal as if lit from within.

Individual crystals are found in well shaped rhombohedrons and more rarely scalahedrons. In a massive form its pink and white bands are extremely attractive and are often used in semi-precious jewelry. Rhodochrosite is often carved into figurines and tubular stalactitic forms are sliced into circles with concentric bands that are truly unique in the mineral kingdom. Fine crystals are sometimes cut into gemstones, but rhodochrosite's softness and brittleness limit it as a gemstone for everyday use.

Identification of rhodochrosite is fairly easy despite a few similarly colored minerals such as rhodonite. Rhodonite is harder and has different cleavage; but perhaps the best distinguishing factor is its lack of reaction to acids. Rhodochrosite will easily with show some reaction to cold acids which demonstrates its carbonate chemistry. Basically, any rose-pink carbonate is considered rhodochrosite; however some calcites with a small amount of manganese impurities can be pink in color. The manganese replaces some of the calciums in calcite but a complete series between calcite and rhodochrosite is not established. Differentiating pink calcite from rhodochrosite may require a fluorescence test as rhodochrosite is distinctly non-fluorescent and manganese is a fluorescent activator in calcite.

There are many localities for rhodochrosite that are of great reknown. Beyond a doubt, the best locality for rhodochrosite is the Sweet Home Mine in Colorado. It is unmatched for its superb rhodochrosite crystals that exhibit the best features of the species; a fine bright rose color and sharp well formed crystals. Some specimens from here are quite large and of world class distinction.

Other localities have produced some fine specimens as well. Catamarca, Argentina has an old inca silver mine that has produced fine stalatitic examples of rhodochrosite that are unique and very attractive. Cut cross-sections reveal concentric bands of light and dark rose colored layers. These specimens are carved and used for many ornamental purposes.

Mont Saint-Hilaire, Quebec, Canada has produced many fine rare minerals but it also produces some nice rhodochrosite specimens as well. Specimens from here are generally small, but have a good color and are associated with rarer minerals.

There are many Peruvian rhodochrosite localities that have produced a number of good specimens. These crystals are usually paler in color than other specimens, but are accented by interesting metal sulfide minerals.
N'Chwanging Mine, Hotazel, South Africa has produced possibly the best examples of scalahedral crystals of rhodochrosite. The unusual crystal habit is due in part to this being one of a few sedimentary crystallizing environments for the species. Most other localities are the result of metamorphism, late stage igneous intrusion or more commonly hydrothermal precipitation.

 

 

PHYSICAL CHARACTERISTICS:

  • Color is red to pink, sometimes almost white, yellow and brown.
  • Luster is vitreous to resinous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is trigonal; bar 3 2/m.
  • Crystal Habits include the rhombohedrons and scalahedrons with rounded or curved faces that can obscure the crystal shape. Some crystals can be flattened to a bladed habit and these are sometimes aggregated into rosettes or minute crystals into spherules. Also botryoidal, globular, stalactitic, layered, nodular, vein-filling and granular. Twinning is somewhat common forming penetration twins and contact twins similar to calcite's twins.
  • Cleavage is perfect in three directions forming rhombohedrons.
  • Fracture is uneven.
  • Hardness is 3.5 - 4.
  • Specific Gravity is approximately 3.5 (above average)
  • Streak is white.
  • Other Characteristics: Pink and white banding in massive forms, non-fluorescence and specimens effervesce easily with dilute acids.
  • Associated Minerals include calcite, ankerite, alabandite, rhodonite, bementite, spessartine, fluorite, manganite, quartz and many metal sulfides.
  • Notable Occurrences are numerous and include the famous Sweet Home Mine, Alma, Park County and American Tunnel, Silverton, Colorado; Butte, Montana; the mines of Franklin, New Jersey; Humboldt Mine, Cochise County, Arizona and many sites in California, USA. Also found in Catamarca, Argentine; Huaron Mine and several mines in Ancash Department, Peru; Kara oba, Kazakhatan; Sacrimb, Transylvania, Romania; Cornwall, England; Harz Mountains, Germany; Tsumeb, Otavi, Namibia; Santa Eulalia and Magdalena, Mexico; N'Chwanging Mine, Hotazel, South Africa; Mont Saint-Hilaire, Quebec, Canada and many other localities from around the world.
  • Best Field Indicators are color, crystal habit, reaction to acid, non-fluorescence and perfect cleavage.

 

 

 

 

 

THE MINERAL RHODONITE

 

  • Chemistry: (Mn, Fe, Mg, Ca)5(SiO3)5 , Manganese Iron Magnesium Calcium Silicate.
  • Class: Silicates
  • Subclass: Inosilicates
  • Group: Pyroxenoid
  • Uses: ornamental and semi-precious stone and as a minor ore of manganese
  • Specimens

Rhodonite is an attractive mineral that is often carved and used in jewelry. It is named after the Greek word for rose, rhodon. Its rose-pink color is distinctive and can only be confused with rhodochrosite and the rare mineral, pyroxmangite, MnSiO3. Rhodochrosite however is streaked with white minerals such as calcite and is reactive to acids. While rhodonite does not react to acids and is usually associated with black manganese minerals and pyrite. Pyroxmangite is a little harder to distinguish because the two minerals are closely related and x-ray studies are usually needed when found massive. Crystals of pyroxmangite are often twinned as is not the case with rhodochrosite crystals. Crystals of rhodonite, while not in nearly the same abundance as massive rhodonite, are still found and distributed on the mineral markets. They come from a few notable localities and are considered classics by collectors.

 

PHYSICAL CHARACTERISTICS:

  • Color is typically pink to red or orange and even black.
  • Luster is vitreous to dull to pearly on polished surfaces.
  • Transparency: Crystals are generally translucent and rarely transparent.
  • Crystal System is triclinic; bar 1
  • Crystal Habits include crystals that have a blocky prismatic habit, however crystals are rare. More typically massive, coarse and fine granular aggregates.
  • Cleavage is perfect in two directions forming prisms with a rectangular cross-section.
  • Fracture is conchoidal.
  • Hardness is 5.5 - 6.5.
  • Specific Gravity is approximately 3.4 - 3.7+ (above average for translucent minerals)
  • Streak is white.
  • Associated Minerals are calcite, pyrite, microcline, spessartine, pyroxmangite and other manganese minerals.
  • Other Characteristics: May tarnish to a brown or black color upon exposure.
  • Notable Occurrences include Ural Mountains, Russia; Broken Hill, Australia; Langban, Sweden, Menas Gerais, Brazil and Massachusetts and Franklin, New Jersey, USA.
  • Best Field Indicators are color, black inclusions, lack of reaction to acid and hardness.

 

 

 

 

 

THE MINERAL RICHTERITE

 


Richterite, which is sometimes called soda tremolite, is closely related to tremolite. It basically is the sodium rich version of tremolite which is calcium rich. Another closely related mineral is ferrorichterite, which has replaced richterite's magnesium with iron. Yet another related mineral is fluororichterite and it is enriched in fluorine by replacing some or all of the hydroxides in richterite. Fluororichterite is also spelled fluorrichterite.

Richterite, ferrorichterite, fluororichterite and tremolite belong to the Amphibole Group of minerals. This is a large group of double chained silicates where chains of silicates are held together by the metal ions sodium, calcium, iron, magnesium, aluminum and sometimes other metals such as manganese, titanium, potassium and lithium. Richterite often contains some manganese, fluorine and potassium and these are sometimes included in its formula or referred to as a variety such as K-richterite or fluor-magnesio richterite. All these similar sounding variety names and related species make for some confusion.

Ricterite is not a common mineral, but is found world wide as a small constituent in unusual rocks. Richterite is found in contact metamorphosed limestones, ultramafic igneous extrusives, metasomatic deposits and alkaline igneous rocks. Its type locality of Langban Mine and Pajsberg, Varmland, Sweden and Kipawa, Quebec, Canada are richterite's only consistent sources of good crystals. When crystals are seen they usually are slender and prismatic with typical amphibole diamond-shaped cross sections. Some richterite has been found in the meteorite debris at Canyon Diablo in Arizona.

 

PHYSICAL CHARACTERISTICS:

  • Color is brown, reddish brown, yellow and light to dark green.
  • Luster is vitreous to dull.
  • Transparency: Crystals are generally translucent, but some specimens are translucent.
  • Crystal System is Monoclinic; 2/m
  • Crystal Habits include long prismatic crystals. Crystals can have a diamond-shaped cross-section although rarely symmetrical. Also found granular, massive and occasionally in radial aggregates.
  • Cleavage is imperfect in two directions at 56 and 124 degrees.
  • Fracture is uneven.
  • Hardness is 5 - 6.
  • Specific Gravity is approximately 2.9 - 3.3 (average for translucent minerals).
  • Streak is brown.
  • Other Characteristics: pleochroic in translucent specimens. Large crystals have an almost striated or grainy appearance.
  • Associated Minerals are quartz, feldspars, aegirine, arfvedsonite, diopside, pectolite, phlogopite, chromite, Iron-nickel, roedderite, kosmochlor, krinovite, tainiolite, calcite, fluorite, svabite, sodalite and eudialyte.
  • Notable Occurrences include the type locality of Langban Mine and Pajsberg, Varmland, Sweden as well as Mont Saint-Hilaire and Kipawa, Quebec, Canada; Myanmar; Madagascar and Leucite Hills, Wyoming and in the meteorite at Canyon Diablo, Arizona.
  • Best Field Indicators are crystal habit (especially cross-section), color and cleavage.

 

 

THE MINERAL RIEBECKITE

 


Riebeckite is not a well known mineral although most people have probably seen stones that at one time were composed of riebeckite crystals. The typically dark blue mineral was named after a famous eighteenth century German explorer and minerologist, Emil Riebeck. Riebeckite is an important mineral for two main reasons: one for when it is there and one for when it isn't.

First, some forms of riebeckite are asbestiform and can be used as asbestos. Asbestos has many industrial uses despite some health risks and is made of different minerals all with a fibrous habit. Serpentine and tremolite form most of the asbestos that is used for industrial purposes. But riebeckite has a variety called "crocidolite" that is asbestiform in habit and is a significant percentage of the total tonage of asbestos that is mined annually. The largest deposit of crocidolite occurs in South Africa and is mined there in large quantities. A second deposit in Australia is significantly smaller but is still productive. Crocidolite is also known as "blue asbestos" and "riebeckite asbestos".

Secondly, crocidolite is often found pseudomorphed by quartz into an attractive ornamental stone. The stone is extremely popular as a semi-precious stone and is known by many trade names such as Tiger's Eye, Hawk's Eye, Falcon's Eye, etc. A pseudomorph is an atom by atom replacement of one mineral for another, without significant destruction of the original mineral's outward shape. The pseudomorphing of riebeckite's asbestos fibers does two things; it preserves the beauty of the fibers and their lustrous light effects and it produces a much more durable stone that is now, thanks to the silicification, suitable for carving and jewelry. Blue tiger's eye has preserved the original blue color of the riebeckite while the more common brown color is the result of some oxidation of the iron into limonite inclusions. Although it is improper to refer to tiger's eye as being a form of riebeckite because there is no riebeckite present in the stone, credit must be given to this mineral for the aid in producing this wonderfully beautiful ornamental stone.

The chemistry of riebeckite is odd in that it includes two different iron atoms. One is ferric (with a plus 3 charge) and one is ferrous (with a plus 2 charge). The ferrous iron occupies the same position as and substitutes with the plus 2 manganese because both ions are of nearly the same size. The formula is written the way it is to show the different iron ions.

Riebeckite is a part of several solid solution series. A solid solution series is where two or more elements can substitute for each other without changing the structure of the mineral. In the case of riebeckite, there exists two such series. The easiest to explain series exists with a mineral called magnesioriebeckite. Riebeckite is the ferrous iron rich member of the series and as the name implies, magnesioriebeckite is the magnesium rich member. Magnesioriebeckite formula, Na2(Mg, Fe)3Fe2Si8O22(OH)2, is nearly identical to riebeckite and so are the properties of the two minerals. Can you spot the difference in the formula?

The other solid solution series is incomplete, meaning there are gaps in the percentages between the minerals. The other members of this series include one that is much more well know than magnesioriebeckite and one that is almost as obscure. The common mineral is glaucophane and its formula is Na2(Mg, Fe)3Al2Si8O22(OH)2. Glaucophane is the magnesium and aluminum rich member and riebeckite is the ferrous and ferric iron rich member. The obscure mineral crossite is the intermediate member of the series. This series is really a series between two series; the Riebeckite Series and the Glaucophane Series. Glaucophane is really the same as magnesioriebeckite, except with aluminums, and riebeckite is the the same as glaucophane's own series partner ferroglaucophane, except with iron. The formulas in the table below are representing the pure state of each mineral for clearity.


THE RIEBECKITE/GLAUCOPHANE SERIES

FERROUS IRON [Fe(+2)] RICH
MAGNESIUM (Mg) RICH
FERRIC IRON [Fe(+3)] RICH
RIEBECKITE
Na2Fe(+2)3Fe(+3)2Si8O22(OH)2
MAGNESIORIEBECKITE
Na2Mg3Fe(+3)2Si8O22(OH)2
intermediate
none defined
CROSSITE
Na2(Mg, Fe(+2))3(Fe(+3), Al)2Si8O22(OH)2
ALUMINUM (Al) RICH
FERROGLAUCOPHANE
Na2Fe(+2)3Al2Si8O22(OH)2
GLAUCOPHANE
Na2Mg3Al2Si8O22(OH)2

All the members of this series have the same structure and similar properties. However, with a increase in iron percentages the color darkens, the streak is bluer, the density increases and the luster increases. Riebeckite is found in alkaline granites, syenites, schists and metamorphosed banded iron formations (BIF). Its presence in igneous rocks is quite different from glaucophane which is restricted for some reason to metamorphic rocks. Asbestos riebeckite is only found in metamorphic rocks, however.

 

PHYSICAL CHARACTERISTICS:

  • Color is usually dark blue to black.
  • Luster is vitreous or silky in fibrous forms.
  • Transparency: Crystals are translucent.
  • Crystal System is monoclinic; 2/m.
  • Crystal Habits include slender prismatic to acicular, often aggregated crystals, columnar, granular and fibrous, asbestiform masses. A moss-like aggregate habit has been described when found in some igneous rocks.
  • Cleavage: is perfect in two directions at 56 and 124 degree angles.
  • Fracture is splintery to uneven.
  • Hardness is 5 - 6.
  • Specific Gravity is approximately 3.2 - 3.4 (average to slightly above average).
  • Streak is blue-gray.
  • Other Characteristics: Weakly pleochroic and crystals are striated lengthwise.
  • Associated Minerals are nepheline, quartz, almandine, aegirine, feldspars, micas and hematite.
  • Notable Occurrences include Socotra Island, South Yemen; Transvaal, South Africa; Schirmeck, Germany; Langesund, Norway; Krivoi Rog, Ukraine; Hamersley Range in Western Australia; Scotland; Madagascar; Quincy, Massachusetts; St Peter's Dome, El Paso County, Colorado; California; Oregon and Cumberland Hill, Rhode Island, USA.
  • Best Field Indicators are crystal habit, color, streak, cleavage and hardness.


 

 

THE MINERAL ROCKBRIDGEITE

 

  • Chemistry: (Fe, Mn)Fe4(PO4)3(OH)5, Iron Manganese Phosphate Hydroxide.
  • Class: Phosphates
  • Uses: Only as mineral specimens.
  • Specimens

Rockbridgeite is one of the more oddly named and yet interesting phosphate minerals. It has a general green color but that changes with oxidation to a dark brown or black. Never-the-less, rockbridgeite shows classic botryoidal form similar to specimens of limonite. In fact, it produces a nice backdrop to the more colorful minerals that may be attached to the rounded botryoidal landscape, such as the sphericules of the lovely pink phosphate mineral strengite.

Rockbridgeite forms from the alteration (oxidation) of primary iron and manganese phosphates. The chemistry of rockbridgeite is odd in that it includes two different iron atoms. One is ferric (with a plus 3 charge) and one is ferrous (with a plus 2 charge). The ferrous iron occupies the same position as and substitutes with the plus 2 manganese. It is this reason that the formula is written the way it is to show the different irons. Geologist and petrologists are very interested in minerals that contain elements with two different oxidation states. It represents a mineral that formed as the oxidation of the original material was taking place and its temperature and pressure of formation can then give clues to the conditions that were present during oxidation.

Rockbridgeite forms a series with the mineral frondelite. A series occurs when two or more elements can freely substitute for each other without significant alteration of the structure. In this case, rockbridgeite is a ferrous iron rich mineral and frondelite is the manganese rich member of the series.

 

 

PHYSICAL CHARACTERISTICS:

  • Color is brown, dark green, yellow-brown or black.
  • Luster is varied from vitreous to dull or earthy.
  • Transparency: Specimens are translucent to transparent.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include prismatic to tabular crystals, but often botryoidal, reniform, encrusting, massive and fibrous.
  • Cleavage is poor.
  • Fracture is uneven.
  • Hardness is 4.5
  • Specific Gravity is approximately 3.4 (slightly above average).
  • Streak is green or brown.
  • Associated Minerals include strengite, beraunite, dufrenite and limonite.
  • Notable Occurrences include Cornwall, England; Siegerland, Germany; Svappavaara, Norrbotten, Sweden; Black Hills, Custer County, South Dakota and South Mountain, Midvale, Rockbridge County (hence the name), Virginia, USA and Brazil.
  • Best Field Indicators are crystal habit, color, associations and streak.



 

 

THE MINERAL ROMANECHITE

 

  • Chemical Formula: Ba(Mn+2, Mn+4)5O10-H2O , Hydrated Barium Manganese Oxide
  • Class: Oxides and Hydroxides
  • Uses: an ore of manganese and as a mineral specimen
  • Specimens

Romanechite is not a well known mineral, but is probably a part of most well rounded mineral collections. It is the primary constituent of psilomelane which is sometimes treated as a mineral and sometimes treated as a mixture of minerals or as a rock. Psilomelane is a mineral name that is losing its significance and romanechite is being used as the name for specimens previously known as psilomelane. However, this might be just as inaccurate since most specimens of psilomelane are not exclusively romanechite. Some mineral books consider romanechite and psilomelane to be synonyms for the same mineral. Here, romanechite is considered the pure form of Ba(Mn+2, Mn+4)5O10-H2O. It therefore differs from psilomelane in density and hardness, both of which are somewhat diminished in the mixture that is psilomelane.

Romanechite is an important ore of manganese. Manganese is a strategically valuable metal since it is an essential ingredient in steel and other alloys. The mining term "wad" is used to indicate ores that are a mixture of several manganese oxides such as psilomelane (romanechite), pyrolusite and others that are difficult to distinguish.

 

 

PHYSICAL CHARACTERISTICS:

  • Color is variable from iron-black to bluish black to steel gray.
  • Luster is submetallic to dull.
  • Transparency crystals are opaque.
  • Crystal System is monoclinic.
  • Crystal Habits include massive, fibrous, botryoidal, columnar, stalactitic, concretionary, powdery and earthy.
  • Cleavage is absent.
  • Fracture is uneven.
  • Hardness is 6.
  • Specific Gravity is 4.7 - 5 (heavy for non-metallic minerals)
  • Streak is brownish black.
  • Associated Minerals are barite, hematite, quartz, pyrolusite and other manganese oxide minerals.
  • Notable Occurances include Austinville, Wythe County., Virginia, Upper Pennisula of Michigan and Tuscon, Arizona, USA; Saxony, Germany; Saone et Loire, France; Cornwall, England; Ouro Preto, Minas Gerias, Brazil and elsewhere.
  • Best Field Indicators are habits, luster, hardness, color and streak.

 

      

THE MINERAL ROSASITE

 

  • Chemistry: (Cu, Zn)2CO3(OH)2 , Copper Zinc Carbonate Hydroxide
  • Class: Carbonates
  • Group: Rosasite
  • Uses: very minor ore of zinc and copper and as a mineral specimen
  • Specimens

Rosasite forms in the oxidation zones of zinc-copper deposits. It typically is found as crusts and botryoidal masses or nodules. Crystals are fibrous and found in tufted aggregates. The color is an attractive bluish green. Rosasite is associated with red limonite and other such colorful minerals as aurichalcite, smithsonite and hemimorphite. Nodules of rosasite certainly add color to what are termed "landscape" specimens.

Rosasite can be confused with Aurichalcite, (Zn, Cu)5 (CO 3 )2(OH)6 . However rosasite is usually more massive but not lamellar. Rosasite crystals are harder than aurichalcite; 4 versus 1 - 2 respectively.

 

PHYSICAL CHARACTERISTICS:

  • Color is usually a bluish-green to green.
  • Luster is silky to vitreous to dull for massive specimens.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is monoclinic; 2/m
  • Crystal Habits include radiating tufts of fibrous crystals. It typically is found as crusts and botryoidal masses or nodules.
  • Hardness is 4
  • Specific Gravity is approximately 4 (somewhat heavy for non-metallic minerals)
  • Cleavage is perfect in one direction but not usually noticed because of fibrous crystal habit.
  • Fracture is fibrous.
  • Streak is pale shades of bluish green or green.
  • Associated Minerals include limonite, smithsonite, hemimorphite, malachite, aurichalcite and calcite.
  • Other Characteristics: Effervesceses easily in cold dilute hydrochloric acid.
  • Notable Occurrences include Arizona, New Mexico and Inyo Co., California, USA; Rosas Mine, Sardinia, Italy; Tsumeb, Namibia and Mapimi, Durango, Mexico.
  • Best Field Indicators are crystal habits, color, associations, hardness and reaction to acid.



 

  

THE MINERAL ROSELITE

 





Roselite is a beautifully colored mineral and varies from rose-red to pink. It would be a misguided assumption that its name came from its color. In fact it is named for a Germany eighteenth century mineralogist, Gustav Rose. The color of roselite comes from the same coloring agent of many different colorful minerals, namely cobalt. Erythrite, of whom roselite is often associated, is also a rose-colored cobalt arsenate and is easily confused with roselite except for the micaceous cleavage of erythrite. Roselite is a popular, although scarce, collection mineral. Its color and small, complex crystals are attractive and make roselite a nice thumbnail mineral.

Roselite is in a solid solution series with the mineral wendwilsonite, (Hydrated Calcium Magnesium Cobalt Arsenate). A solid solution series is a situation in which two or more elements are able to occupy the same position in the structures of two or more minerals. In this case, the two elements are cobalt and magnesium and they can replace each other in the roselite/wendwilsonite structure. If the particular crystal is rich in cobalt, then the mineral is roselite; if the crystal is rich in magnesium, then the mineral is wendwilsonite.

Roselite is dimorphous with the much rarer, but sometimes associated mineral beta-roselite. Beta-roselite is triclinic instead of monoclinic in symmetry like roselite. The symmetry difference is due to a different structure, yet the two minerals have the same formula. This is why they are called dimorphous (di means two; morph means shape).

Roselite lends its name to a small group of rather obscure minerals called the Roselite Group. The Roselite Group is a group of monoclinic, hydrated calcium arsenates with a general formula of Ca2X(AsO4)2 - 2H2O The X in the formula can be either cobalt, manganese, magnesium and/or zinc.
These are the members of the Roselite Group:
  • Brandtite (Hydrated Calcium Manganese Magnesium Cobalt Arsenate)
  • Roselite (Hydrated Calcium Cobalt Magnesium Arsenate)
  • Wendwilsonite (Hydrated Calcium Magnesium Cobalt Arsenate)
  • Zincroselite (Hydrated Calcium Zinc Arsenate)

 

PHYSICAL CHARACTERISTICS:

  • Color is rose-red to dark pink (lighter shades with decreasing cobalt content).
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is monoclinic; 2/m.
  • Crystal Habits include small prismatic to tabular, often complex, crystals and spherical aggregates and massive crusts. Twinning is the norm and just adds to the complexity of the crystals.
  • Cleavage is perfect in one direction.
  • Fracture is uneven.
  • Hardness is 3.5
  • Specific Gravity is approximately 3.5 - 3.7 (above average for translucent minerals).
  • Streak is light red.
  • Associated Minerals are erythrite, beta-roselite and limonite.
  • Notable Occurrences include Rappold Mine, Schneeberg, Saxony and Shapbach, Germany and Bou Azzer, Morocco.
  • Best Field Indicators are color, crystal habit, streak, cleavage, density and associations with cobalt ores.




        

RUBY, the red variety of corundum


VARIETY INFORMATION:

  • VARIETY OF: Corundum , Al2O3 .
  • USES: Gemstone.
  • BIRTHSTONE FOR: July
  • COLOR: various shades of red.
  • INDEX OF REFRACTION: 1.76 - 1.78
  • BIREFRINGENCE: 0.009
  • HARDNESS: 9
  • CLEAVAGE: none, although there is a rhombic parting
  • CRYSTAL SYSTEM: trigonal
  • PLEOCHROIC: strongly
  • For natural ruby mineral specimens see our For Sale or Sold lists
Ruby is the red variety of corundum, the second hardest natural mineral known to mankind. The non-red variety of corundum is Sapphire Sapphires are well known among the general public as being blue, but can be nearly any color. The red color in ruby is caused by trace amounts of the element chromium. The best shade of red for ruby is often given the name "pigeon blood red", but ruby can be any shade of red up to almost pink.

Oriented rutile crystal inclusions cause a six-rayed-star light effect (called asterism) to form the popular Star Ruby.
Rubies come from all over the world but good gemstones are found at Thailand, India, Madagascar, Zimbabwe, North Carolina in the U.S., Afghanistan, Pakistan, Sri Lanka, Kenya, Tanzania, Kampuchea, and perhaps most notably, Burma.
Rubies have a famous place in science - the first lasers were made from artificial ruby crystals.  They still are used for this purpose although other materials offer improved efficiency.  Some ruby crystals show the fluorescence (actually very short term phosphorescence) that makes a laser possible.


 

             

THE MINERAL RUTILE

 


Rutile is an interesting, varied and important mineral. Rutile is a major ore of titanium, a metal used for high tech alloys because of its light weight, high strength and resistance to corrosion. Rutile is also unwittingly of major importance to the gemstone markets. It also forms its own interesting and beautiful mineral specimens.

Microscopic inclusions of rutile in quartz, tourmaline, ruby, sapphire and other gemstones, produces light effects such as cat's eye and asterisms (stars). A beautiful stone produced by large inclusions of golden rutile needles in clear quartz is called rutilated quartz. Rutilated quartz is sometimes used as a semi-precious stone and/or for carvings. This stone is produced because at high temperatures and pressure, n(SiO2)-n(TiO2) is in a stable state but as temperatures cool and pressure eases the two separate with rutile crystals trapped inside the quartz crystals.

Twinning is common in rutile crystals, with a cyclic twin forming that is comprised of six or even eight "twins" arranged in a circle. A Rutile Star is a formation of crystals of rutile in a six rayed orientation. The crystals grow off of a hematite crystal and the orientation is caused by its six rhombic faces.

 

PHYSICAL CHARACTERISTICS:

  • Color is black or reddish brown in large thick crystals or golden yellow or rusty yellow as inclusions or in thin crystals.
  • Luster is adamantine to submetallic.
  • Transparency: Crystals are transparent in rather thin crystals otherwise opaque.
  • Crystal System is tetragonal; 4/m 2/m 2/m
  • Crystal Habits include eight sided prisms and blocky 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. Crystals with some twins forming hexagonal or octahedral circles. A very common habit is thin acicular needles (especially as inclusions in other minerals) or as blades.
  • Cleavage is good in two directions forming prisms, poor in a third (basal).
  • Fracture is conchoidal to uneven.
  • Hardness is 6 - 6.5
  • Specific Gravity is 4.2+ (slightly heavy)
  • Streak is brown
  • Other Characteristics: Striations lengthwise on crystals, high refractive index (2.63) gives it a sparkle greater than diamond (2.42).
  • Associated Minerals are quartz, tourmaline, barite, hematite and other oxides and silicates.
  • Notable Occurrences include Minas Gerias, Brazil; Swiss Alps; Arkansas, USA and some African locallities.
  • Best Field Indicators are crystal habit, streak, hardness, color and high index of refraction (luster).

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