Wednesday, August 24, 2011

Mineral S


THE MINERAL SAFFLORITE

 


Safflorite is a rare mineral, but is found with other arsenides and thus it is included with them when mined for cobalt and/or arsenic. When weathered it is associated with the pink to red cobalt arsenate mineral erythrite. This is good because safflorite lacks other good distinguishing characteristics, especially from the closely related lollingite and other arsenic sulfides. Lollingite has more iron than cobalt in its chemistry. Another closely related mineral is rammelsbergite, which has more nickel than cobalt. These minerals represent the three most common members of the Lollingite Group. This group is sometimes placed in the larger Marcasite Group.

Safflorite is a near dimorph with the mineral clinosafflorite. A dimorph is a set of two minerals that share the same chemistry but have different structures. In this case clinosafflorite's formula is (Co, Fe, Ni)As2. Not quite an exact dimorph with the addition of the nickel, but safflorite often contains traces of nickel, just not as much. Clinosafflorite gets its name by virtue of its monoclinic symmetry compared to safflorite's orthorhombic symmetry (inclined safflorite, in other words). Twinning is common in safflorite and forms star shaped trillings. Cobalt minerals are sometimes interesting to collect and safflorite is certainly interesting.

 

PHYSICAL CHARACTERISTICS:

  • Color is tin white (darkens upon exposure to air).
  • Luster is metallic.
  • Transparency: Crystals are opaque.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include tiny tabular to prismatic crystals and fibrous masses (sometimes radially fibrous). Also compact and massive. Twins are seen as star shaped trillings.
  • Cleavage is indistinct.
  • Fracture: Conchoidal.
  • Hardness is 4.5 - 5
  • Specific Gravity is approximately 6.9 - 7.4 (well above average for metallic minerals)
  • Streak is a black.
  • Associated Minerals include arsenic, cobaltite, arsenopyrite, skutterudite, calcite and erythrite.
  • Notable Occurrences include Schneeburg, Harz Mountains, Germany; Great Bear Lake, Ontario, Canada; Lafayette County, Wisconsin and Oregon, USA; Javornik, Czech Republic and the type locality of Nordmark, Varmland, Sweden.
  • Best Field Indicators are crystal habits, color (dark tarnish), associations, streak, hardness and density.

 

 

THE MINERAL SAINFELDITE

 

  • Chemistry: Ca5(AsO4)2(AsO3{OH})2 - 4H2O, Hydrated Calcium Arsenate Hydroxide.
  • Class: Phosphates
  • Subclass: Arsenates
  • Uses: Only as mineral specimens.
  • Specimens

Sainfeldite is a rare mineral but is becoming a popular collection mineral. It forms nice rosette clusters of crystals with an attractive pink color. Although the crystals are usually small, they do provide a good sparkle and make for good specimens.

Sainfeldite's chemistry is unusual in that it has the unusual ion group of AsO3{OH}. This group is the same as the regular arsenate ion group except that one of the four oxygens is replaced by an hydroxide or OH group. Sometimes the formula for sainfeldite is written as Ca5H2(AsO4)4 - 4H2O. Other arsenates with this chemical oddity include pharmacolite, guerinite and picropharmacolite, all of which are associated with sainfeldite. The mineral hureaulite is similar, but with a phosphate as the affected ion group.

 

PHYSICAL CHARACTERISTICS:

  • Color is mostly a pale pink, white or colorless.
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is monoclinic; 2/m
  • Crystal Habits include small prismatic crystals with slanted pinacoidal faces sometimes in radiating clusters or rosettes.
  • Cleavage is absent.
  • Fracture is uneven
  • Hardness is 4
  • Specific Gravity is approximately 3.0 (slightly above average for translucent minerals).
  • Streak is white.
  • Associated Minerals are pharmacolite, guerinite, picropharmacolite and other secondary arsenates.
  • Notable Occurrences include Richelsdorf, Germany and Ste. Marie-aux-Mines, Alsace, France.
  • Best Field Indicators are color, locality, associations and crystal habit.




 

THE MINERAL SAL AMMONIAC

 

  • Chemistry: NH4Cl, Ammonium Chloride.
  • Class: Halides
  • Uses: As mineral specimens.
  • Specimens

Sal ammoniac is certainly an oddball mineral. It is composed of ammonium, NH4, and this alone is odd enough. Sal ammoniac is one of the most common and most well known of the ammonium-bearing minerals. These are some other ammonium bearing-minerals:
  • Boussingaultite (Hydrated Ammonium Magnesium Sulfate)
  • Cryptohalite (Ammonium Silicon Fluoride)
  • Guanine (Carbohydrate Ammonium Nitrogen Oxide)
  • Struvite (Hydrated Ammonium Magnesium Phosphate)
  • Tschermigite (Hydrated Ammonium Aluminum Sulfate)

Sal ammoniac forms on volcanic rocks near fume releasing vents. There is no liquid phase as the mineral crystallizes from these fumes in a process called sublimation. The crystallization occurs as the gases are escaping and crystals tend to be short-lived. Sal ammoniac is very soluble in water and crystals will be removed during the first rain of their existence, so to speak, if they are not removed by collectors first.

Other possible natural occurrences exist from underground burning coal seams. Alexander the Great is said to have found sal ammoniac crystals in a cave in a region that is now Tadzhikistan. The region was plagued by underground burning coal seams.

Sal ammoniac can be produced artificially and has its uses. When ammonia fumes are blown across hydrochloric acid; sal ammoniac fumes are produced. The technique is sometimes used to produce sal ammoniac coatings on dark objects that are about to be photographed. This will often enhance a difficult to photograph object by adding detail to the subject.

Natural crystals of sal ammoniac have an unreal or unnatural character to them. They are so small, delicate, intricate and at times quite beautiful that they just do not seem to be like other minerals. But it is sal ammoniac's natural methods of origin that lend themselves to produce these one-of-a-kind specimens.

 

PHYSICAL CHARACTERISTICS:

  • Color is colorless, white or off-white almost yellow.
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System: Isometric; possibly of the gyroidal class 4 3 2.
  • Crystal Habits include cubes, octahedrons and dodecahedrons. Complicated arborescent, snowflake-like and dendritic specimens are available. Crusts and coatings are more common.
  • Cleavage is poor in one direction.
  • Fracture is conchoidal to earthy.
  • Hardness is 1.5 - 2
  • Specific Gravity is 1.5 (very light).
  • Streak is white.
  • Associated Minerals include sodium alum, sulfur and other fumarole minerals.
  • Notable Occurrences include Tadzhikistan; Mt. Vesuvius, Italy and Paricutin Volcano, Michoacan, Mexico.
  • Best Field Indicators are crystal habit, associations, origin of formation, softness and density.

 

 

 

THE MINERAL SAMARSKITE-(Y)

 

  • Chemical Formula: (Y, Ce, U, Fe)3(Nb, Ta, Ti)5O16, Yttrium Cerium Uranium Iron Niobium Tantalum Titanium Oxide.
  • Class: Oxides and Hydroxides
  • Uses: A minor ore of rare earth elements and uranium, sometimes cut as a gemstone and as mineral specimens.
  • Specimens

Samarskite, whose exact name is samarskite-(Y) (the Y is for the yttrium), is one of several Rare Earth Oxides. These rare earth oxides form from the leftover elements that other minerals seem to not want. Other rare earth oxides such as fergusonite and euxenite have very similar properties to samarskite and are often associated with each other, compounding the problem. Even the common oxide, rutile, is almost indistinguishable from these rare earth oxides without chemical tests when rutile is found massive.

Samarskite is found in rare earth rich granite pegmatites, a slow cooling igneous intrusive rock. Samarskite is associated with quartz, feldspars, columbite, tantalite and other rare earth minerals. Samarskite is common enough and locally abundant enough that it has potential to be a valuable resource for its rare earth metals. But it is its gemstone use that is what is odd about this mineral. Samarskite can be cut into attractive gems and used as cabochons, although since the stones are slightly radioactive, their use as wearable gemstones should be quite ...well...risky!

As mineral specimens, samarskite can be a nice addition to one's collection. Good crystals are rare, but prized when found. Although the color is usually just a velvety black the luster is generally high and striking. Remember, this is a radioactive mineral and should be stored away from other minerals that are subject to damage from radioactivity and of course human exposure should be limited !

 

PHYSICAL CHARACTERISTICS:

  • Color is dark pithchy to velvety black to dark brown.
  • Luster is vitreous to resinous and fresh surfaces can have a submetallic luster.
  • Transparency: Crystals are nearly opaque.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include stubby prismatic crystals often embedded in the matrix of the host pegmatite; as well as granular and massive.
  • Cleavage is poor in one direction.
  • Fracture is conchoidal.
  • Hardness is 5 - 6
  • Specific Gravity is approximately 4.3 - 5.87 (heavy for non-metallic minerals). Extreme variation caused by variable composition of component metals.
  • Streak is reddish brown.
  • Other Characteristics: Radioactive and crystals/specimens are often coated with a limonite like earthy coating.
  • Associated Minerals include quartz, feldspars, euxenite, fergusonite, monazite, columbite, tantalite, allanite, gadolinite, and zircon
  • Notable Occurrences include the Ural Mountains of Russia also found in Iveland, Satersdalen, Norway; Sweden; Divino de Uba, Minas Gerias, Brazil; Madagascar and Mitchell County, North Carolina, California, Maine, Colorado and Connecticut, USA.
  • Best Field Indicators are luster, fracture, color, streak, radioactivity, associations, environment and specific gravity.

 

   

THE MINERAL SANBORNITE

 


Sanbornite is a rare, but nicely named, phyllosilicate mineral. It is one of just a few barium minerals; other more common barium minerals being barite and witherite. Barium tends to be a rather difficult element to place in minerals due to its large ionic size. Barium has an ionic radius of 1.34 Angstroms compared to the much more easily accommodated calcium's 0.99 Angstroms. Barium's high density (its atomic number is 56) usually give minerals that possess it a higher than normal specific gravity. Sanbornite has a pearly luster and flashes of iridescence and can be a nice addition to someone's collection.

 

PHYSICAL CHARACTERISTICS:

  • Color is usually a pale green, also gray, white or colorless.
  • Luster is pearly to vitreous or dull.
  • Transparency: Crystals are transparent to mostly translucent.
  • Crystal System is orthorhombic.
  • Crystal Habits include flat tabular or lamellar crystals.
  • Cleavage is good in one direction.
  • Fracture is uneven.
  • Hardness is 5
  • Specific Gravity is approximately 3.8 (above average for a non-metallic mineral)
  • Streak is white.
  • Other Characteristics: Displays iridescence between cleavage layers and lamellar twining is common.
  • Notable Occurrences are limited to Trumball Peak, Mariposa County and Big Creek, Fresno County, California, USA.



               

SANIDINE

 


Sanidine is a polymorph of other minerals that share the same chemistry but have different crystal structures. If positive identification between these minerals can not be made by field methods then the specimen may simply be refered to as a potassium feldspar or K-spar. Plagioclase feldspars lack potassium, are light colored and are usually striated. The other k-spar minerals are orthoclase, microcline and anorthoclase.

The differences between these minerals are minor in hand samples. Microcline tends to be deeper colored and is the only one that can be, but is not always, a deep green (amazonite). Sanidine does not show the lamellar twinning that is common in microcline and is occassionally present as striations on cleavage surfaces.

Sanidine and anorthoclase usually have a flattened crystal habit. Other than that, environment of formation is the only other hand sample clue to distinguish orthoclase from sanidine. Sanidine (and anorthoclase) are a common constiuent in extrusive igneous rocks such as rhyolites, where the rock cooled quickly. Orthoclase is the main k-spar of granites and syenites that cooled somewhat more slowly, and microcline is the k-spar associated with granites, pegmatites, and syenites that cooled slowly. Optical properties and x-ray techniques are the only good ways to distinguish sanidine from orthoclase, microcline and anorthoclase.

Sanidine is the high temperature form of the k-spars. Above approximately 900 degrees C, sanidine is the stable structure. Between approximately 500 degrees C and 900 degrees C, orthoclase is the stable structure. And, at 400 degrees C or less, microcline is the stable structure for KAlSi3O8. The difference between the structures is only in the randomness of the aluminums and silicons. In microcline the ions are ordered and this produces the lower symmetry of triclinic (yes, higher more order produces lower symmetry, see discussion in symmetry). With higher temperatures the positions of the aluminums and silicons become more disordered and produce the monoclinic symmetry of orthoclase and finally sanidine.

Twinning is common in all feldspars and follow certain twin laws such as the Albite Law, the Pericline Law, the Carlsbad Law, the Manebach Law and the Baveno Law. In sanidine only the Carlsbad Law, the Manebach Law and the Baveno Law are seen. The Carlsbad Law twin produces what appears to be two intergrown crystals growing in opposite directions. Two different twin laws, the Manebach and Baveno laws, produce crystals with one prominant mirror plane and penetrant angles or notches into the crystal. Although twinning in general is common for sanidine, single crystals showing a perfect twin are rare and are often collected by twin fanciers.

Sanidine is an end member of a series of the alkali or K-feldspars whose series ranges from pure NaAlSi3 O8 to pure KAlSi3 O8. This series only exists at high temperatures with the mineral sanadine being the potassium, K, rich end member and albite being the sodium, Na, rich end member. Anorthoclase is the intermediate k-spar at about 10 to 36% sodium content.

 

PHYSICAL CHARACTERISTICS:

  • Color is off-white, yellow or pale shades of other colors.
  • Luster is vitreous to dull if weathered.
  • Transparency: crystals are transparent to translucent
  • Crystal System is monoclinic; 2/m
  • Crystal Habits include tabular crystals. Crystals have a nearly rectangular cross-section with slightly slanted dome and pinacoid terminations. Also as rounded phenocrysts in volcanic rocks Twinning is common. (see above).
  • Cleavage is good in 2 directions forming nearly right angled prisms.
  • Fracture is conchoidal or uneven
  • Hardness is 6
  • Specific Gravity is approximately 2.56 - 2.53 (average)
  • Streak is white.
  • Associated Minerals are plagioclase feldspars, micas and other minerals found as phenocrysts in volcanic rocks.
  • Notable Occurrences Germany; Colorado and New Mexico, USA; Russia; Italy and others.
  • Best Field Indicators color, luster, lack of striations, cleavage, twinning if present and occurrence in volcanic rocks.



 

 

SAPPHIRE,

the non-red variety of corundum

 

VARIETY INFORMATION:

  • VARIETY OF: Corundum , Al2O3 .
  • USES: Gemstone.
  • BIRTHSTONE FOR: September
  • COLOR: various colors, except for 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 sapphire mineral specimens see our For Sale or Sold lists
Sapphire is the non-red variety of corundum, the second hardest natural mineral known to mankind. The red variety of corundum is Ruby. Sapphires are well known among the general public as being blue, but it can be nearly any color, even colorless. White (or colorless but massive) sapphire would more properly be called corundum. The blue color is by far the most popular color for sapphire but orange-pink, golden, white, and even black have generated much interest in the gem trade. Oriented rutile crystal inclusions cause a six-pointed-star light effect (called asterism to form the popular Star Sapphire. 



    

THE MINERAL SARTORITE

 


Sartorite is another rare sulfide mineral from the famous quarry at Lengenbach, Binnental, Valais, Switzerland. Most of the more exotic minerals from this site are arsenic sulfides and sulfosalts like sartorite. Some of the rare minerals from here include: novakite, seligmannite, rathite, jordanite, smythite, wallisite, lengenbachite, bernardite, baumhauerite, arsenolamprite, liveingite, dufrenoysite, marrite, imhofite and hatchite to name a few. Sartorite is usually a steel gray mineral with a nice luster and striated acicular to prismatic crystals embedded in a dolomitic marble. It is a rare mineral and is only found at Lengenbach.

 

PHYSICAL CHARACTERISTICS:

  • Color is a steel gray, lead gray to black.
  • Luster is metallic.
  • Transparency: Crystals are opaque.
  • Crystal System: Monoclinic; 2/m.
  • Crystal Habits include acicular to prismatic deeply grooved or striated crystals with a steep pinacoidal face; also in massive and granular forms.
  • Cleavage is good in one direction.
  • Fracture: Conchoidal.
  • Hardness is 3.
  • Specific Gravity is 5.1 (slightly heavier than average for metallic minerals)
  • Streak is dark brown.
  • Associated Minerals include dolomite, realgar and baumhauerite.
  • Notable Occurrences are limited to the type locality, the Lengenbach Quarry, Binnental, Valais, Switzerland.
  • Best Field Indicators are crystal habit, locality, lack of internal reflections, grooves and striations, associations, cleavage and density.

 

 

 

 

THE MINERAL SERIES, SCAPOLITE

 


Scapolite is actually the name of a series between the sodium chloride rich mineral called marialite and the calcium carbonate rich mineral meionite. The structure of scapolite is similar to some feldspathoids in that it is composed of large open spaces in the framework of silicate and aluminum tetrahedrons. These open spaces are large enough to essentially cage the very large ionic groups of either Na4Cl or Ca4CO3. The sulfate ion shown in the formula is typically barely more than a trace, but is found in far greater percentages than the occasional fluorine or hydroxide interlopers in the scapolite structure.

Scapolite forms in metamorphic rocks from the alteration of plagioclase feldspars. The entire scapolite series is analogous to the plagioclase series. If the formula of marialite is written as 3(Na(Al, Si)4O8)NaCl it is clear how well it matches the formula of the sodium rich plagioclase, albite, NaAlSi3O8. A similar look at meionite's formula, 3(Ca(Al, Si)4O8)CaCO3, shows that it too is near three times the formula of anorthite, CaAl2Si2O8. The addition of the extra sodium chloride or calcium carbonate occurs during metamorphism as well as substantial alteration of the structure. Although nearly pure albite and anorthite specimens are sometimes found, pure forms of meionite and marialite are unknown of in nature.

Distinguishing the scapolite minerals from each other is difficult as they differ only slightly in density and index of refraction, increasing in both with increasing calcium content. It is because of this closeness in properties and yet seemingly very different chemistries that scapolite has had its share of pseudonyms. Wernerite was the most common alternate name for the scapolite series, but now it has mostly disappeared from use. A few other names such as mizzonite and dipyre as well as marialite and meionite have been used as names for the entire scapolite series. Now scapolite is a name recognized by most every mineralogist and rock hound the world over.

Scapolite, which is Greek for "shaft", is commonly found in stubby to long prismatic crystals, hence the name. It is tetragonal so that it will commonly have a square or octahedral cross-section. It belongs to a rather exclusive symmetry class that is shared by only two other well known minerals, powellite and scheelite. The symmetry class is called the Tetragonal Dipyramidal Class and is characterized by only having the one primary four fold axis of rotation and a perpendicular mirror plane, denoted as 4/m. Unfortunately, scapolite rarely forms crystals with the complex faces that would be needed to see this unusual symmetry.

As a gemstone scapolite is not well known, but can be very attractive. The color of its gemstones, which is usually a nice yellow to orange, pink or violet, is its best feature as its fire and hardness are somewhat lacking. Less transparent material can often be cut as cabochons that will often exhibit a good Cat's Eye effect or if the "Cat's Eye" is not distinct enough it will show a play of light similar to Moonstone.

 

PHYSICAL CHARACTERISTICS:

  • Color is most commonly white, colorless, greenish or gray but also yellow, brown, reddish, pink, violet or blue colors are possible.
  • Luster is vitreous on freshly exposed crystals or surfaces but weathering causes a dulling of the luster.
  • Transparency: Crystals are translucent to transparent.
  • Crystal System: Tetragonal; 4/m
  • Crystal Habits include prismatic to stocky crystals terminated by a pyramid. Complete crystals are rare and often the crystals will have distorted shapes with uneven faces.
  • Cleavage is distinct in several prismatic directions producing a splintery almost fibrous appearance in cleaved massive specimens.
  • Fracture is subconchoidal to uneven.
  • Hardness is 5.5 - 6
  • Specific Gravity is 2.5 - 2.7 (average)
  • Streak is white.
  • Other Characteristics: Will often fluoresce either orange, yellow or more rarely red under ultraviolet light and index of refraction varies from 1.54 to 1.60.
  • Associated Minerals include hornblende, the garnet minerals almandine and andradite, actinolite, microcline, pyroxenes, apatite, andalusite, zircon, sphene, diopside and muscovite.
  • Notable Occurrences include Renfrow Co., Ontario; Franklin, New Jersey, Massachusetts and St Lawrence Co., New York, USA; Arendel, Norway; Mount Vesuvius, Italy and Mexico. Gemstone sources are found in Minas Gerias, Brazil; Madagascar, Tremorgio, Switzerland and Burma.
  • Best Field Indicators include color, crystal habit, cleavage surface features, fluorescence and hardness.





 

      

THE MINERAL SCHEELITE

 

  • Chemistry: CaWO4, Calcium Tungstate
  • Class: Sulfates
  • Subclass: Tungstates
  • Uses: An important source of tungsten, rarely cut as gemstones and as mineral specimens.
  • Specimens

Scheelite is an important ore of tungsten which is a strategically important metal. Scheelite is named for the discoverer of tungsten, K. W. Scheele. Although most of the world wide production of tungsten comes from the mineral wolframite, scheelite is especially abundant in the US and provides the United States with most of its supply.
Scheelite is a popular mineral for collectors. It forms perfect tetragonal dipyramidal crystals that look very much like octahedrons. These pseudo-octahedral crystals are sometimes truncated with minor pyramids, but only on the top and/or bottom points of the crystal; giving evidence of their true symmetry. Other minerals that form pseudo-octahedral crystals similar to scheelite include wardite, anatase and powellite.

Powellite, CaMoO4, is isostructural with scheelite which is why it forms similar crystals. The two minerals form a series in which the tungsten of scheelite is substituted for by the molybdenum of powellite. Powellite fluoresces a yellow color while scheelite fluoresces a bright blue under short wave ultraviolet light. Of course since molybdenum can substitute for tungsten, some scheelite specimens will show a yellow fluorescence.

The crystals of scheelite can look like fluorite octahedrons which can also fluoresce. However, fluorite has perfect octahedral cleavage and a lower luster. Massive scheelite has often been mistaken for massive quartz, but then the fluorescence of scheelite is a dead giveaway.

Many prospectors for scheelite have made good use of scheelite's typically bright blue fluorescence by searching for scheelite deposits by night with ultraviolet lamps. Many old mines have even been reopened after examination of the mine shafts with ultraviolet lamps have proven that the ore is not quite yet exhausted.

 

PHYSICAL CHARACTERISTICS:

  • Color is white, yellow, orange or greenish gray to brown.
  • Luster is adamantine to greasy.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is tetragonal; 4/m
  • Crystal Habits include the pseudo-octahedral crystals that are actually tetragonal dipyramids. Also massive and granular.
  • Cleavage is indistinct in two directions and good in another (dipyramidal).
  • Fracture is conchoidal.
  • Hardness is 4.5 - 5.
  • Specific Gravity is approximately 5.9 - 6.1 (very heavy for translucent minerals).
  • Streak is white.
  • Other Characteristics: Fluoresces blue (yellow with molybdenum traces) under short wave ultraviolet light.
  • Associated Minerals are quartz, garnets, vesuvianite, epidote, topaz, schorl, apatite, gold, silver, molybdenite, cassiterite, wolframite and fluorite.
  • Notable Occurrences include Hollinger Mine, Ontario, Canada; Saxony, Germany; Tong Wha, Korea; Brazil; Sonora, Mexico; Cornwall, England; New South Wales and Queensland, Australia and Mill City, Nevada, Atolia, San Bernardino Co., California, Cochise Co., Arizona, Utah and Colorado, USA.
  • Best Field Indicators are crystal habit, color, density, luster and especially its fluorescence.

THE MINERAL SCHMITTERITE

 


Schmitterite is a very rare tellurium mineral. The type locality for schmitterite, Moctezuma Mine, Moctezuma, Sonora, Mexico, is famous for rare telllurium minerals. Chemically schmitterite is doubly noteworthy as it is also a uranyl mineral. The uranyl ion group, UO2, is unusual in that it is positively charged (+2). Most ionic groups, especially those that contain oxygen are negatively charged such as the sulfate ion group, SO4-2; carbonate ion group, CO3-2; borate ion group, BO3-3; phosphate ion group, PO4-3; tellurite ion group, TeO3-2 and the silicate ion group, SiO4-4. Because the uranyl ion group is positively charged some minerals do not require isolated metal ions and are thus composed of only ion groups such as the uranyl ionic group and the tellurite ionic group of schmitterite. Another positively charged ion group is the ammonium ion group, NH4+1, found in the minerals sal ammoniac, cryptohalite, tschermigite guanine, struvite and larderellite to name a few. Schmitterite 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 colorless to yellowish.
  • Luster is pearly.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is orthorhombic; 2/m 2/m 2/m.
  • Crystal Habits include small granular crystals and massive.
  • Cleavage is good in one direction.
  • Hardness is 1.
  • Specific Gravity is approximately 6.8 - 6.9 (very heavy for translucent minerals).
  • Streak is white.
  • Other Characteristics: Specimens are somewhat radioactive.
  • Associated Minerals include various other tellurium minerals such rodalquilarite, emmonsite and other tellurates and tellurites.
  • Notable Occurrences are limited to the type locality of Moctezuma Mine and the Bambollita Mine of Moctezuma, Sonora, Mexico.
  • Best Field Indicators are locality,softness, high density, luster, radioactivity and cleavage.




THE MINERAL SCHOLZITE

 

  • Chemistry: CaZn2(PO4)2 - 2H2O , Hydrated Calcium Zinc Phosphate.
  • Class: Phosphates
  • Uses: Only as mineral specimens.
  • Specimens

Scholzite is a rare zinc phosphate mineral and comes from the classic phosphate mineral locality at Hagendorf, Bavaria, Germany. The Hagendorf locality contains a phosphate rich pegmatitic intrusive body that has undergone a certain amount of alteration. Rare minerals such as scholzite are a generous gift from this famous mineral site. Scholzite forms nice bright white tabular crystals and is associated with other rare phosphates. Specimens can be especially nice when combined with other rare minerals.
Scholzite is dimorphous with the mineral parascholzite. A dimorph is a mineral that has the same chemistry but different structures. The even rarer parascholzite is monoclinic while scholzite is orthorhombic in regards to structural symmetry.

 

PHYSICAL CHARACTERISTICS:

  • Color is white, colorless, gray or pale yellow.
  • Luster is vitreous.
  • Transparency crystals are transparent to translucent.
  • Crystal System is orthorhombic.
  • Crystal Habits include acicular to more commonly tabular crystals, often radiated.
  • Cleavage is indistinct.
  • Fracture is conchoidal
  • Hardness is 3 - 4
  • Specific Gravity is approximately 3.1 (slightly above average for translucent minerals)
  • Streak is white.
  • Associated Minerals include hopeite, parahopeite, phosphophyllite, tarbuttite, quartz and other pegmatitic minerals.
  • Notable Occurrences are limited to Hagendorf, Bavaria, Germany and Reaphook Hill, South Australia.
  • Best Field Indicators are crystal habit, associations, lack of distinct cleavage, locality and color.

 

 

 

 

         

THE MINERAL SCHORL

 

  • Chemistry: NaFe3(Al,Fe)6Si6O18(BO3)3(OH)4, Sodium Iron Aluminum Boro-silicate Hydroxide.
  • Class: Silicates
  • Subclass: Cyclosilicates
  • Group: Tourmalines
  • Uses: mineral collection specimens, electrical uses and as ornamental stone.
  • Specimens

Schorl is the most common mineral in the Tourmaline Group. Some other members of the Tourmaline Group are elbaite, uvite, buergerite and dravite. All tourmalines form similar crystals because they are isostructural, meaning that they share the same internal crystalline structure.

Schorl can form some very nice classic tourmaline crystals. Tourmaline crystals are interesting because they are hemimorphic, having a different shaped top from the bottom of the crystal. Some crystals of Schorl can reach a rather large size and can display a great variety of crystal faces.

Schorl can be a major component of igneous and metamorphic rocks. Although it is not the only black mineral common to such rocks, it is the only one that will form crystals with a clear triangular cross-section.

Long thin crystals of schorl are common as inclusions in quartz, forming the ornamental stone called "Tourmalinated Quartz". This stone is unique with its long needle to straw sized, arrow straight, prismatic crystals of pitch black schorl criss-crossing the clear colorless quartz. This attractive stone is used in semi-precious jewelry, carved figurines, obelisks, crystal balls, eggs and as a popular tumbled stone.

 

PHYSICAL CHARACTERISTICS:

  • Color is black.
  • Luster is vitreous to submetallic.
  • Transparency: crystals are opaque.
  • Crystal System is trigonal; 3 m.
  • Crystal Habit is typically elongated three sided prisms. The terminations can be either a simple to complex trigonal pyramid or flat basal face. The prism faces are usually striated lengthwise. In cross section, all tourmalines will appear predominantly triangular in shape. Doubly terminated crystals are hemimorphic meaning that the two ends of the crystal are not exactly alike. Massive forms can also be found.
  • Cleavage is absent although there is basal parting.
  • Fracture is uneven to conchoidal.
  • Hardness is 7 - 7.5
  • Specific Gravity is 3.2+ (slightly heavier than average)
  • Streak is white.
  • Other Characteristics: Piezoelectric.
  • Associated Minerals include those minerals associated with granitic pegmatites and metamorphic rocks such as micas, feldspars and quartz.
  • Notable Occurrences include Brazil; Colorado; Appalachian mountains; Germany; Cornwall, England and many others.
  • Best Field Indicators are crystal habit, overall triangular cross-section, striations, color and hardness.

 

 

THE MINERAL SCHROCKINGERITE

 

  • Chemistry: NaCa3UO2SO4(CO3)3F - 10H2O, Hydrated Sodium Calcium Uranyl Sulfate Carbonate Fluoride.
  • Class: Carbonates
  • Uses: As a very insignificant source of uranium and as mineral specimens.
  • Specimens

Schrockingerite, also spelled schroeckingerite and schrokingerite, is one of the few uranyl carbonate minerals that is found on the mineral markets. Other uranyl carbonates include andersonite, rutherfordine, sharpite, liebigite, swartzite and bayleyite. Schrockingerite in addition to having a uranyl (UO2) group in its chemistry, has a sulfate ion. Schrockingerite could be classified as a sulfate, but is here classified as a carbonate due to the greater number and therefore greater significance of the carbonate ions. Other sulfate carbonates include susannite, leadhillite, hanksite, macphersonite, wherryite and caledonite. The fact that schrockingerite is a uranyl sulfate carbonate though makes it very rare. Schrockingerite forms as a secondary mineral and is also found on cave and mine walls.

 

PHYSICAL CHARACTERISTICS:

  • Color is yellow-green.
  • Luster is vitreous to pearly.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is triclinic.
  • Crystal Habits include pseudohexagonal platy crystals and encrustations.
  • Cleavage is perfect in one direction.
  • Hardness is 2.5.
  • Specific Gravity is 2.5 - 2.6 (slightly below average for a translucent mineral)
  • Streak is slightly off-white.
  • Other Characteristics Some specimens are fluorescent.
  • Associated Minerals include clays, gypsum, johannite, andersonite, swartzite and bayleyite and other secondary uranium minerals.
  • Notable Occurrences include the type locality of Jachymov, Zapadocesky kraj, Czech Republic as well as the Miller Ranch deposit, Kern County, California; Hillside Mine, Yavapai County, Arizona and Lost Creek, Sweetwater, Wyoming, USA; La Soberania Mine, San Isidro, Mendoza, Argentina.
  • Best Field Indicators: Crystal habit, color, associations, fluorescence and locality.



 

THE MINERAL SCOLECITE

 


Though somewhat rare, scolecite is a popular mineral among collectors. It forms in volcanic bubbles called vesicles along with other zeolites. Scolecite's sprays of radiating crystals are, well . . . , exotic, inspiring, awesome, magnificant, etc. They are truly hard to describe, but are something that everyone who loves minerals will enjoy.
Scolecite's structure has a typical zeolite openness about it that allows large ions and molecules to reside and actually move around inside the overall framework. The structure contains open channels that allow water and large ions to travel into and out of the crystal structure. The size of these channels controls the size of the molecules or ions and therefore a zeolite like scolecite can act as a chemical sieve. Scolecite's structure contains aligned chains of silicate tetrahedrons. This produces the needle-like crystals and the cleavage results from the weaker bonds between the chains.

Scolecite, a calcium zeolite, natrolite, a sodium zeolite, and mesolite, a calcium and sodium zeolite, are closely related and sometimes found together. The presence of calcium in two of the minerals slightly alters the structure from that of natrolite; from an orthorhombic symmetry to a monoclinic symmetry. However, twinning of scolecite and mesolite often make them look orthorhombic All three minerals are referred to as "chain" or "needle" zeolites. They are similar and hard to distinguish when in clusters with radiating, acicular habits. Natrolite tends to forms thin crystals with pyramidal terminations, but mesolite's fibrous crystals are usually the thinnest crystals of the three minerals. Scolecite's larger crystals tend to be more robust and durable. These characteristics are only generalities and can not be used as dependable identifying traits. Absolute identification can not be made by ordinary means.

 

PHYSICAL CHARACTERISTICS:

  • Color is clear or white.
  • Luster is vitreous to silky.
  • Transparency: crystals are transparent to translucent.
  • Crystal System is monoclinic; 2/m
  • Crystal Habits include sprays of thin acicular crystals with slanted terminations. Also occurs in radiating fibrous clusters.
  • Cleavage is perfect in two directions, prismatic. Cleavage is hard to see due to small crystal size.
  • Fracture is conchoidal.
  • Hardness is 5.
  • Specific Gravity is approximately 2.2 (very light)
  • Streak is white.
  • Associated Minerals are quartz, apophyllite, babingtonite, heulandite, stilbite and other zeolites.
  • Notable Occurrences include Poona, India; Riverside Co., California; Iceland; Skye Scotland and Santa Catarina, Brazil.
  • Best Field Indicators are crystal habit, hardness, density and associations.

 

 

 

 

THE MINERAL SCORODITE

 


Scorodite is an attractive and colorful mineral. It forms in the upper oxidation zones of arsenic rich ore bodies. The ore bodies in which scorodite is usually found contain the mineral arsenopyrite, FeAsS. Scorodite has also been found as a crust precipitated on the outer rims of hot springs.

Crystals of scorodite can form dipyramids that look like octahedrons. These pseudo-octahedral crystals will also resemble the much harder gem mineral zircon. The color of scorodite is variable but it is most known and revered for its bright green or blue colors that really establish scorodite as a wonderful display mineral.

 

PHYSICAL CHARACTERISTICS:

  • Color is colorless, white, green, blue, yellow and brown.
  • Luster is vitreous to sub-adamantine or greasy.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include pseudo-octahedral crystals that are actually orthorhombic dipyramids. Also tabular crystals and fibrous and crusty coatings.
  • Cleavage is very poor in a few directions.
  • Fracture is conchoidal.
  • Hardness is 3.5 - 4.
  • Specific Gravity is approximately 3.1 - 3.3 (average for translucent minerals).
  • Streak is white.
  • Other Characteristics: Soluble in hydrochloric acid.
  • Associated Minerals are arsenopyrite, limonite, adamite, olivenite, arseniosiderite and other oxidation zone minerals.
  • Notable Occurrences include the famous mines at Mapimi, Mexico; also Lavrion, Greece; Ouro Preto, Minas Gerias, Brazil; Cornwall, England; Tsumeb, Namibia; Ontario; California, USA and Zacatecas, Mexico.
  • Best Field Indicators are color, luster, non-fluorescent, associations and crystal habits.



 

THE MINERAL SCORZALITE

 

  • Chemistry: (Fe, Mg)Al2(PO4)2(OH)2, Iron Magnesium Aluminum Phosphate Hydroxide.
  • Class: Phosphates
  • Uses: mineral specimens and ornamental stone.
  • Specimens

Scorzalite is a rare phosphate mineral. It was only recognized as a distinct mineral in the last 50 years. Scorzalite is in a solid solution series with the mineral lazulite. A solid solution series is a set of two or more minerals that have a couple of elements that substitute freely for each other. The lazulite-scorzalite series ranges from the magnesium rich lazulite to the iron rich scorzalite. The rarer scorzalite does not differ appreciably, except that it tends to be darker, less transparent and denser than lazulite.

 

PHYSICAL CHARACTERISTICS:

  • Color is dark azure-blue.
  • Luster is vitreous to dull.
  • Transparency: Specimens are translucent.
  • Crystal System: is monoclinic; 2/m
  • Crystal Habits include a dipyramidal form that comes close to looking like a distorted octahedron, usually flattened to the point of being a tabular crystal. Also granular and massive.
  • Cleavage is distinct in one direction.
  • Fracture is uneven.
  • Hardness is 6.
  • Specific Gravity is approximately 3.4 (above average for translucent minerals).
  • Streak is pale blue.
  • Associated Minerals are quartz, rutile, kyanite, andalusite, garnets, muscovite, corundum, wardite, brazilianite and siderite.
  • Other Characteristics: Only slightly soluable in warm hydrochloric acid.
  • Notable Occurrences: Menas Gerias, Brazil and most localities that contain lazulite will have some crystals of scorzalite.
  • Best Field Indicators: are dark blue color, poor reaction to acids, crystal habit, slightly higher density than lazulite, associations and localities.

 

 

 

       

THE MINERAL GYPSUM

 

  • Chemistry: CaSO4-2(H2O), Hydrated Calcium Sulfate
  • Class: Sulfates
  • Uses: plaster, wall board, some cements, fertilizer, paint filler, ornamental stone, etc..
  • Specimens
Gypsum is one of the more common minerals in sedimentary environments. It is a major rock forming mineral that produces massive beds, usually from precipitation out of highly saline waters. Since it forms easily from saline water, gypsum can have many inclusions of other minerals and even trapped bubbles of air and water.
Gypsum has several variety names that are widely used in the mineral trade.
  • "Selenite" is the colorless and transparent variety that shows a pearl like luster and has been described as having a moon like glow. The word selenite comes from the greek for Moon and means moon rock.
  • Another variety is a compact fiberous aggregate called "satin spar" . This variety has a very satin like look that gives a play of light up and down the fiberous crystals.
  • A fine grained massive material is called "alabaster" and is an ornamental stone used in fine carvings for centuries, even eons.

 

PHYSICAL CHARACTERISTICS:

  • Color is usually white, colorless or gray, but can also be shades of red, brown and yellow.
  • Luster is vitreous to pearly especially on cleavage surfaces.
  • Transparency crystals are transparent to translucent.
  • Crystal System is monoclinic; 2/m
  • Crystal Habits include the tabular, bladed or blocky crystals with a slanted parallelogram outline. The pinacoid faces dominate with jutting prism faces on the edges of the tabular crystals. Long thin crystals show bends and some specimens bend into spirals called "Ram's Horn Selenite" Two types of twinning are common and one produces a "spear head twin" or "swallowtail twin" while the other type produces a "fishtail twin". Also massive, crusty, granular, earthy and fiberous.
  • Cleavage is good in one direction and distinct in two others..
  • Fracture is uneven but rarely seen.
  • Hardness is 2 and can be scratched by a fingernail.
  • Specific Gravity is approximately 2.3+ (light)
  • Streak is white.
  • Associated Minerals are halite, calcite, sulfur, pyrite, borax and many others.
  • Other Characteristics: thin crystals are flexible but not elastic, meaning they can be bent but will not bend back on their own. Also some samples are fluorescent. Gypsum has a very low thermal conductivity (hence it's use in drywall as an insulating filler). A crystal of Gypsum will feel noticeably warmer than a like crystal of quartz.
  • Notable Occurances include Naica, Mexico; Sicily; Utah and Colorado, USA; and many other locallities throughout the world.
  • Best Field Indicators are crystal habit, flexible crystals, cleavage and hardness.



 

THE MINERAL NATIVE SELENIUM

 


Selenium is a very rare mineral. It is scarce wherever it is found and it is not found too often. The color is a distinctive red-gray with a metallic luster. This is quite different from its closest related element, sulfur, which is vitreous and yellow. It is more similar in color to native tellurium which follows selenium in the same Periodic Table of Elements column. Elements found in the same column of the Periodic Table of Elements tend to have similar properties although those properties also tend to strengthen or diminish either up or down the column.

8 O
OXYGEN
16 S
SULFUR
34 Se
SELENIUM
52 Te
TELLURIUM
84 Po
POLONIUM
On the left is the column from the Periodic Table of Elements in which selenium appears. The farther down the column, the more metallic in character the element becomes. So that oxygen is the least metallic and polonium is the most metallic of the elements in this column. The dividing line between metals and non-metals is between selenium and tellurium; making these elements semi-metals, an element that has significant characteristics of both metals and non-metals. Tellurium is more metallic in nature than selenium but is still a semi-metal.
Although selenium has a metallic luster, it is not metallic in crystal structure or bonding characteristics. Its bonds are more covalent in nature and its structure is more spread out than in metallic minerals such as copper and iron. Both of these elements have lighter atoms than selenium and yet in crystalline form each is nearly twice the density of crystalline selenium. With metallic bonded crystals, atoms are comparatively much closer and are nearly in contact with each other with respect to covalently bonded crystals.

The element selenium has many industrial uses. Most notable is the use of selenium for photvoltaic and photoconductive purposes. This makes it valuable for use in photoelectric cells and exposure meters for photographic purposes. Selenium is also a good tracer element for medical purposes and as a isotope tracer in ground water for hydrogeologic purposes since there are as many as six stable natural isotopes of selenium. The more isotopes, the more control a scientist has over aberrant abundances.
Most elemental selenium comes from the refining of copper sulfides as selenium is a common trace element in these minerals. There is no real ore of selenium as these minerals, including native selenium, are far too rare. These are some other minerals that contain selenium as a major component:


  • Berzelianite (Copper Selenide)
  • Clausthalite (Lead Selenide)
  • Eucairite (Silver Copper Selenide)
  • Hakite (Copper Mercury Silver Antimony Selenium Sulfide)
  • Klockmannite (Copper Selenide)
  • Palladseite (Palladium Selenide)
  • Penroseite (Nickel Selenide)
  • Selen-tellurium (Selenium Tellurium)
  • Tiemannite (Mercury Selenide)
  • Umangite (Copper Selenide)

Selenium the mineral, or native selenium, does not usually form good crystals but when it does they are steep rhombohedrons or tiny acicular (hair-like) crystals. Massive specimens are also known. Selenium is an interesting element that rarely forms good specimens. A specimen of good quality is therefore a real treat for a collector of native elements.

 

PHYSICAL CHARACTERISTICS:

  • Color is reddish-gray to red.
  • Luster is metallic.
  • Transparency is opaque.
  • Crystal System is trigonal; bar 3 2/m
  • Crystal Habits include steep rhombohedrons or tiny acicular (hair-like) crystals. Massive specimens are also known..
  • Streak is gray.
  • Hardness is 2
  • Specific Gravity is 4.8 (average for metallic minerals).
  • Notable Occurrences include Jerome, Yavapai County, Arizona; Gold Quarry Mine and Willard Mine, Nevada and the Darwin Mine, California, USA; Moctezuma, Sonora, Mexico; Monte Vesuvius, Italy; Harz Mountains, Germany; Potosi, Bolivia and Los Llantenes, Argentina.
  • Best Field Indicators are color, density, hardness and locality.

 

 

 

 

 

     

THE MINERAL SEMSEYITE

 

  • Chemistry: Pb9Sb8S21, Lead Antimony Sulfide.
  • Class: Sulfides
  • Subclass: Sulfosalts
  • Group: Fuloppite
  • Uses: As mineral specimens and as a very minor ore of lead.
  • Specimens
Semseyite forms interesting aggregates of intergrown tabular crystals that are rather unique. The mineral is named for an Hungarian mineral collector, A. Semsy. Semseyite is another rare sulfosalt, a segment of sulfides where the antimony acts more like a metal than a non-metal and occupies a position where it is bonded to sulfurs. Semseyite is also one of several lead antimony sulfides, an informal group of similar minerals. Some of these minerals belong to the formal group of minerals known as the Fuloppite Group. These minerals are rather similar in characteristics and are difficult to distinguish from one another. Other members of the Fuloppite Group include fuloppite, plagionite, heteromorphite and rayite.

 

PHYSICAL CHARACTERISTICS:

  • Color is gray to black.
  • Luster is metallic.
  • Transparency: Crystals are opaque.
  • Crystal System: Monoclinic; 2/m.
  • Crystal Habits include radial to spherical aggregates of tabular nearly parallel crystals.
  • Cleavage is perfect in several oblique directions.
  • Hardness is 2.5
  • Specific Gravity is 5.8 - 6.1 (heavier than average for metallic minerals)
  • Streak is black.
  • Associated Minerals include quartz, pyrite, stibnite and several other rare sulfosalts.
  • Notable Occurrences are limited to the type locality of Baia Sprie, Maramures, Romania as well as the Glendinning Antimony Mine, Glenshanna Burn, Dumfrieshire, Scotland; France and Turkey
  • Best Field Indicators are crystal habit, associations, density and cleavage.

 

 

 

 

THE MINERAL SENARMONTITE

 


Senarmontite is, in some respects, an under appreciated mineral. It is rather scarce and not very well distributed, so good specimens are hard to find. It forms excellent octahedral crystals that can be transparent with a high luster. Specimens with dozens of octahedrons of randomly varying sizes are especially admirable.

Senarmontite is dimorphous with the mineral valentinite. Both minerals have the exact same chemistry, but they have different structures. Senarmontite is isometric and valentinite is orthorhombic. It is similar to the situation between diamond and graphite. Valentinite is associated with senarmontite as well as stibnite. Actually both senarmontite and valentinite are oxidation products of the antimony sulfide.

 

PHYSICAL CHARACTERISTICS:

  • Color is colorless, white or gray.
  • Luster is vitreous, adamantine, greasy or resinous.
  • Transparency: Crystals are translucent to transparent.
  • Crystal System is isometric.
  • Crystal Habits typically include well formed octahedral crystals but more commonly massive as well as granular and encrusting.
  • Cleavage is imperfect.
  • Fracture is conchoidal.
  • Hardness is 2 - 2.5
  • Specific Gravity is approximately 5.3 - 5.5 (heavier than average).
  • Streak is white.
  • Associated Minerals include quartz, stibnite , valentinite, kermesite, native antimony, stibiconite and other antimony minerals.
  • Notable Occurrences are limited to the Djebel-Haminate Mine, Ain Beida, Qacentina (Constantine), Algeria and Ham Sud Township, Wolfe County, Quebec, Canada.
  • Best Field Indicators are crystal habit, high luster, associations and specific gravity.

 

 

    

THE MINERAL SERANDITE

 

  • Chemistry: Na(Mn, Ca)2Si3O8(OH), Sodium Manganese Calcium Silicate Hydroxide
  • Class: Silicates
  • Subclass: Inosilicates
  • Uses: Only as mineral specimens.
  • Specimens

Serandite has a beautiful pink color that is only similar to only a few other minerals. Serandite is probably the most famous of the unique minerals found at the Mont. St. Hilaire, Quebec, Canada. It forms nice crystals that are often associated with other rare and interesting minerals. One of the best assortments includes the pink, elongated serandite with attached rounded, snow white analcime crystals. Classic specimens of this mineral assemblage are truly treasured by their owners.

Serandite forms a series with the mineral pectolite, NaCa2Si3O8(OH). The structures are similar but serandite has a significant percentage of manganese ions which substitute for a portion of the calciums in the pectolite. It is the manganese ions which cause the pink color of serandite. Several other manganese minerals have a distinct pink color such as the carbonate rhodochrosite and the silicates rhodonite and inesite. However serandite's color is more of a salmon pink the these pink minerals and it has a silky luster that is distinct.

 

PHYSICAL CHARACTERISTICS:

  • Color is pink to reddish pink and off white.
  • Luster is vitreous to silky.
  • Transparency crystals are transparent to translucent.
  • Crystal System is triclinic; bar 1
  • Crystal Habits include prismatic crystals with a distorted hexagonal cross-section. Also massive and compact.
  • Cleavage is perfect in two directions at close to right angles.
  • Fracture is splintery due to the cleavage.
  • Hardness is 4.5
  • Specific Gravity is approximately 3.2 - 3.4 (above average for translucent)
  • Streak is white.
  • Associated Minerals include calcite, analcime, vesuvianite, grossular garnetand many extremely rare minerals.
  • Notable Occurrences include the famous mines at St. Hilaire, Quebec, Canada and Roma Island, Los Islands, Guinea.
  • Best Field Indicators are crystal habit, color, luster, associations, locality and cleavage.


 

   

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 SHATTUCKITE

 

  • Chemistry: Cu5(SiO3)4(OH)2, Copper Silicate Hydroxide
  • Class: Silicates
  • Subclass: Inosilicates
  • Uses: A very minor ore of copper and as an ornamental stone.
  • Specimens

Shattuckite is a relatively rare copper silicate mineral. It was first discovered in the copper mines of Bisbee, Arizona, specifically the Shattuck Mine (hence the name). It is a secondary mineral that forms from the alteration of other secondary minerals. At the Shattuck Mine, it forms pseudomorphs after malachite. A pseudomorph is an atom by atom replacement of a crystal structure by another crystal structure, but with little alteration of the outward shape of the original crystal. Pseudomorph is Greek for "false shape".

Shattuckite, like other copper minerals especially secondary copper minerals, has a very attractive color and is used as an ornamental stone when found massive. Shattuckite's beautiful blue color is its best asset. It can take a good polished and makes nice cabochons, carvings or simple polished stones. Aggregates of shattuckite are also attractive when found as spherules or sprays of deep blue acicular radial crystal clusters. Shattuckite is also found with other rare and/or attractive secondary minerals such alamosite, azurite, "bisbeeite" ( a variety of chrysocolla), luddenite, fornacite , cerussite, malachite, limonite and standard chrysocolla.

 

PHYSICAL CHARACTERISTICS:

  • Color is a unique deep blue.
  • Luster is dull to vitreous.
  • Transparency specimens are translucent to opaque.
  • Crystal System is orthorhombic.
  • Growth Habits include acicular to thin prismatic crystals often found as spherules or sprays of acicular radial crystal clusters. Other habits include massive, fibrous and compact. Also found as pseudomorphs of other secondary minerals such as malachite.
  • Cleavage is perfect in two directions.
  • Fracture is uneven.
  • Hardness is 3.5.
  • Specific Gravity is approximately 4.1 (rather heavy for a non-metallic mineral)
  • Streak is blue.
  • Associated Minerals are quartz, gold, limonite, azurite, malachite, alamosite, azurite, "bisbeeite" ( a variety of chrysocolla), luddenite, fornacite , cerussite, chrysocolla and other secondary copper minerals.
  • Notable Occurrences are limited to the Shattuck Mine (hence the name), Bisbee, Arizona, USA and a few other secondary copper deposits.
  • Best Field Indicators are color, crystal habit, density, locality and associations.



 

  

THE MINERAL SIDERITE

 

  • Chemistry: FeCO3, Iron Carbonate.
  • Class: Carbonate.
  • Group: Calcite.
  • Uses: A minor ore of iron and as mineral specimens.
  • Specimens

Siderite is named for the Greek word for iron, sideros. The word siderite is used in a number of rarer minerals and except in the fact that they all contain iron, they are otherwise unrelated to siderite. They include: Alumopharmacosiderite, arseniosiderite, barium-alumopharmacosiderite, barium-pharmacosiderite, chalcosiderite, erythrosiderite, pharmacosiderite, phosphosiderite and sodiumpharmacosiderite. A variety of siderite forming sphericules is known as sphaerosiderite.

Siderite forms series with the closely related minerals rhodochrosite, MnCO3 and magnesite, MgCO3. These minerals can have some substitution of their metal ions and the cutoff between them and siderite is at 50% iron. Sometimes variety names are given to intermediate members of these minerals such as mangansiderite for an iron rich rhodochrosite or magniosiderite for a magnesium rich siderite. But this can be confusing.

Siderite is roughly the equivalent of calcite but with iron replacing the calcium. The iron has little effect on most structural properties such as cleavage and crystal form; but does effect properties such as density, color, hardness and electro-chemical properties. Siderite is fairly easy to distinguish from calcite by its higher specific gravity and hardness and less vigorous reaction to acids. It can be difficult to distinguish from dolomite however.
Siderite and calcite can form similar crystal habits, although siderite is far less diverse. The typical habit for siderite is the rhombohedron. Most of the time crystals are found in the standard rhomb shape but noticeably flattened rhombs and rhombs with curved surfaces are also well known. Other typical habits include the scalahedron, crusts, sphericules, concretions and complicated botyroidal masses. Siderite forms mostly in sedimentary and hydrothermal environments, although it is also found in some igneous pegmatites.

Siderite is a common mineral although excellent, attractive crystal specimens are sometimes hard to find. But many crystals, when colorfully iridescent, make a wonderful, colorful, satiny, shimmering mineral specimen. The iridescence is probably caused by a surface alteration to the iron oxide, goethite. Further alteration of siderite crystals can result in pseudomorphs. The amorphous iron oxide limonite, forms pseudomorphs that are complete replacements of siderite crystals. Siderite can be a nice collection mineral. It comes in just enough of a variety of crystal forms and colors that make collecting this mineral very interesting.

 

PHYSICAL CHARACTERISTICS:

  • Color is gray, yellow, yellowish brown, greenish-brown, reddish brown and brown. Some specimens show an iridescence probably caused by surface alteration to goethite.
  • Luster is vitreous to pearly or silky in some specimens.
  • Transparency: Crystals are usually translucent or virtually opaque.
  • Crystal System is trigonal; bar 3 2/m.
  • Crystal Habits are commonly curved rhombohedrons that are sometimes flattened to appear bladed, rarely scalahedral. Many aggregate forms are also found such as botryoidal, sphericules (sphaerosiderite), concretionary, stalactitic, vein-filling and earthy.
  • Cleavage is perfect in 3 directions forming rhombs.
  • Fracture is conchoidal to uneven.
  • Hardness is fairly variable going from 3.5 - 4.5.
  • Specific Gravity is 3.9+ (relatively heavy)
  • Streak is white.
  • Other Characteristics: Becomes magnetic when heated, effervesces slightly in contact with strong acids or with warm acids.
  • Associated Minerals include iron sulfides and quartz, cerussite, ankerite, dolomite, goethite, cryolite, limonite, barite, pyrite and sphalerite.
  • Notable Occurrences are numerous and include the Harz Mountains, Germany; several mines in Cornwall, England as well as Peru; Biera Baixa, Portugal; Tatasi, Bolivia; Minas Gerais, Brazil; Lorraine, France; Bohemia, Czech Republic; Broken Hill, New South Wales, Australia; Tsumeb, Otavi, Namibia; the mines of Franklin, New Jersey; San Bernardino County, California; Flambeau Mine, Ladysmith, Wisconsin, Antler Mine, Arizona and Connecticut, USA and Rapid Creek, Yukon Territory; Francon Quarry, Montreal and Mont Saint-Hilaire, Quebec, Canada.
  • Best Field Indicators are crystal habit, slight reaction to acids, cleavage, color and higher than average density.



        

THE MINERAL SILICON

 

  • Chemistry: Si, Elemental Silicon
  • Class: Elements
  • Subclass: Semi-metals
  • Group: Carbon
  • Uses: As an integrated circuit (IC) substrate and semiconductor.
  • Specimens

Silicon is rarely found in nature in its uncombined form. In fact it is amazing how rare native silicon is with 25.7% of the Earth's crust being silicon. Silicon, binds strongly with oxygen and is nearly always found as silicon dioxide, SiO2 (quartz), or as a silicate (SiO4-4). Silicon has been found as a native mineral only in volcanic exhalations and as tiny inclusions in gold.

Of growing interest in rock shops, however, are laboratory-grown silicon boules. Most such specimens are end fragments or flawed discards from the integrated circuit industry. Silicon boules are grown (pulled) from a molten state from a seed crystal, in such a way as to produce a single large crystal which must be completely without crystal defects, or the entire boule must be discarded. Modern techniques can create a single crystal several feet long and up to 10 inches in diameter. These large crystals are sliced into very thin wafers, upon which complex integrated circuits can be etched. The unused parts of the boule are often saved, and used as paperweights or sometimes cut into bookends or other decorative items.

The word silicon (which is taken from the latin word for flint) can be confused with other terms. One of these terms was already mentioned: Silicate (SiO4-4). Silicates are minerals whose primary cation is the SiO4-4 ion group. Another confusing term is silica. Silica is a term used by geologists for SiO2 or silicon dioxide in any form whether it is in the form of quartz, or any of the Quartz Group members, or as a segment of the chemistry of a silicate, or even as silicon dioxide dissolved in water. A geologist might use the phrase, "The magma was rather poor in silica." Indicating an SiO2 content that was lower than expected. Yet another term is silicone. Silicone is a synthetic polymer that is made of silicon, carbon and oxygen and has many medical and some industrial purposes.

 

PHYSICAL CHARACTERISTICS:

  • Color is iron-black, dark silver-gray to bluish brown.
  • Luster is metallic.
  • Transparency: Crystals are opaque.
  • Crystal System is isometric; 4/m bar 3 2/m
  • Crystal Habits are limited to microscopic crystals and inclusions.
  • Cleavage is absent.
  • Fracture is conchoidal.
  • Hardness is 7.
  • Specific Gravity is approxiamtely 2.3.
  • Streak is black
  • Other Characteristics:
  • Associated Minerals are limited to gold in which silicon has been found as inclusions.



  

 THE MINERAL SILLIMANITE

 

  • Chemistry: Al2 SiO5, Aluminum Silicate
  • Class: Silicates
  • Subclass: Nesosilicates
  • Uses: in the manufacture of spark plugs etc, rarely as a gemstone and as mineral specimens.
  • Specimens

Sillimanite is a polymorph with two other minerals; kyanite and andalusite. A polymorph is a mineral that shares the same chemistry but a different crystal structure with another, or other, minerals. Sillimanite is the rarest of the three trimorphs. A variety of sillimanite is called "fibrolite". It is a common fiberous massive form.

 

PHYSICAL CHARACTERISTICS:

  • Color is white, brown and green.
  • Luster is silky when fiberous or vitreous otherwise.
  • Transparency crystals are transparent to translucent.
  • Crystal System is Orthorhombic; 2/m2/m2/m
  • Crystal Habits include rare prismatic crystals but mostly fiberous masses.
  • Cleavage is good in one direction lengthwise.
  • Fracture is splintery.
  • Hardness is 7.5 in large crystals but more fiberous forms are softer.
  • Specific Gravity is approximately 3.2+ (above average)
  • Streak is white.
  • Associated Minerals are garnets, biotite, feldspars, quartz, kyanite and andalusite.
  • Other Characteristics: fibers are brittle distinguishing them from asbestos.
  • Notable Occurrences include Brazil, New England area and many European sites.
  • Best Field Indicators are crystal habit, color, brittlness and hardness if not fiberous.

 

             

NATIVE SILVER

 

  • Chemistry: Ag, Elemental silver
  • Class: Elements
  • Group: Gold
  • Uses: Minor ore of silver for use in jewelry, coins and photographic films and other industrial uses.
  • Specimens

Silver has been mined for eons and has always been popular in jewelry and for coinage. Only in the past hundred years however, has the demand for silver been so great. The reason for this demand is the use of silver in the photography industry, which takes advantage of silver's reactivity to light. Native Silver is rare and much silver is produced from silver-bearing minerals such as prousite, pyrargyrite, galena, etc. Specimens of Native Silver usually consist of wires that are curved and intertwined together, making an inspiring mineralogical curiosity.

 

PHYSICAL CHARACTERISTICS:

  • Color is silver white with exposed specimens tarnishing black.
  • Luster is metallic.
  • Transparency is opaque.
  • Crystal System is isometric; 4/m bar 3 2/m
  • Crystal Habits include massive and disseminated grains, wires and plates as the most common, whole individual crystals are extremely rare but when present are usually cubes, dodecahedrons and octahedrons. "Jack Frost" type crystal growth as shown on some specimens produces beautiful intricate structures. Wires can form coiled clusters that resemble rams horns.
  • Cleavage is absent.
  • Fracture is jagged.
  • Streak is silver white.
  • Hardness is 2.5-3.
  • Specific Gravity is variable according to purity 10-12 (well above average even for metallic minerals)
  • Associated Minerals are silver minerals such as acanthite and prousite, cobaltite, copper, zeolites and quartz.
  • 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; Cobalt, Ontario; Chile; and Germany.
  • Best Field Indicators are color, tarnish, ductility and crystal habit.  

 

 

 

 

THE MINERAL SINHALITE

 


Sinhalite is rare mineral and known only from the gem gravels in Sri Lanka. It was thought to be a brownish variety of the normally green peridot, the gem variety of olivine. It was first discovered to be a new species in 1952 when an unusually dark brown specimen came under scientific scrutiny. Since then it has been an unusual gemstone, being a member of the borates. Because it is so rare, has few notable characteristics to give it distinction and the not too overwhelming demand for brownish green gemstones; sinhalite has not enjoyed much success on the gemstone markets and is usually sought after only by collectors of rare and unusual gemstones. Sinhalite gets its name from sinhala, the Sanskrit word for the island of Ceylon, now known as Sri Lanka.

 

PHYSICAL CHARACTERISTICS:

  • Color is greenish brown to brown, sometimes greenish-yellow.
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is orthorhombic.
  • Crystal Habits are quite limited to alluvial grains found in gem gravels.
  • Cleavage is distinct in two directions.
  • Hardness is 6.5
  • Specific Gravity is approximately 3.5 (slightly above average for translucent minerals)
  • Streak is white.
  • Other Characteristics: strongly pleochroic, meaning it may appear to have different colors from different viewing angles.
  • Associated Minerals are other gem gravel minerals such as ruby, sapphire, peridot and garnets.
  • Notable Occurrences are limited to the gem gravels of Sri Lanka.
  • Best Field Indicators are color, locality, pleochroism and the relatively high hardness.

THE MINERAL SJOGRENITE

 

  • Chemistry: Mg6Fe2CO3(OH)16 - 4H2O, Hydrated Magnesium Iron Carbonate Hydroxide.
  • Class: Carbonate.
  • Group: Manasseite.
  • Uses: Only as mineral specimens.
  • Specimens

Sjogrenite, which is also spelled sjoegrenite, is a very rare mineral from the famous mines of Langban, Varmland, Sweden. It was discovered there and therefore Langban is called its type locality. Sjogrenite is also found at Sterling Hill, New Jersey; Healdsburg, Sonoma County, California and at Kovdor, Kola Peninsula, Russia.

Sjogrenite is dimorphous with the mineral pyroaurite. Dimorphs are minerals that share the same chemistry but have different structures. Sjogrenite is a hexagonal mineral, while pyroaurite is a trigonal mineral.

 

PHYSICAL CHARACTERISTICS:

  • Color is usually white, yellowish, brownish, greenish to off-white.
  • Luster is vitreous to pearly.
  • Transparency: Crystals are usually translucent to transparent.
  • Crystal System is hexagonal; 6/m 2/m 2/m.
  • Crystal Habits include tabular, scaley to platy crystals; also found in fibrous forms.
  • Cleavage is perfect in one direction (basal).
  • Hardness is 2.5.
  • Specific Gravity is 2.1 (very light).
  • Streak is white.
  • Associated Minerals includes tetra-ferriphlogopite, dolomite, pyroaurite, calcite, forsterite, brucite, ludwigite and serpentine.
  • Notable Occurrences include the type locality of Langban, Varmland, Sweden as well as Sterling Hill, New Jersey; Healdsburg, Sonoma County, California, USA and at Kovdor, Kola Peninsula, Russia.
  • Best Field Indicators are crystal habits, cleavage, color and locality.



 

 

THE MINERAL SKLODOWSKITE

 

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

Sklodowskite is a rare uranium mineral that forms from the oxidation of uranium-bearing minerals. Found in good crystals only at one mine at the world famous copper and uranium locality of Shaba, Zaire, the Musonoi Mine produces some of the finest sklodowskite specimens. The mineral is named for the famous chemist Marie Sklodowska Curie, who discovered the element Radium. Its green-yellow to yellow velvety tufts are attractive and make for an unusual mineral specimen. Although less brilliantly colored than its cousins cuprosklodowskite and uranophane, sklodowskite is still 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 green-yellow to yellow.
  • Luster is vitreous to silky.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System: Monoclinic
  • Crystal Habits are typically fibrous tufts and crusts. Also acicular crystals in radial aggregates.
  • Cleavage: perfect in one direction.
  • Hardness is 2 - 3.
  • Specific Gravity is approximately 3.5+ (above average for translucent minerals)
  • Streak is pale yellow.
  • Associated Minerals are uraninite, cuprosklodowskite and Uranophane.
  • Other Characteristics: Radioactive and fluorescent.
  • Notable Occurrences include Musonoi Mine, Shaba, Zaire and Crook Co., Wyoming, USA.
  • Best Field Indicators are crystal habit, color, locality, radioactivity and fluorescence.



 

THE MINERAL SKUTTERUDITE

 

  • Chemistry: CoAs3, Cobalt Arsenide
  • Class: Sulfides
  • Uses: a minor ore of Cobalt and Nickel
  • Specimens

Fine Skutterudite specimens have only recently had widespread distribution on the mineral market. Its pyrite-like crystal forms contrast with its silver color giving it a unique look that is a must for a serious mineral collector.

Skutterudite is the cobalt-rich end member of a series (Smaltite, Chloanthite, or Ferro-Arsenite) in which Nickel or Iron replaces part of the Cobalt. Enough nickel is usually present to make Skutterudite a significant ore of Nickel. The iron rich variety is rare.

 

PHYSICAL CHARACTERISTICS:

  • Color is tin white to silver.
  • Luster is metallic.
  • Transparency crystals are opaque.
  • Crystal System is isometric; bar 3 2/m
  • Crystal Habits include the octahedron often modified with cube faces and the pyritohedron; often in a massive form.
  • Cleavage is indistinct.
  • Fracture is conchoidal or uneven.
  • Hardness is 6.
  • Specific Gravity is approximately 6.5 - 6.8 (heavier than average for metallic minerals)
  • Streak is black.
  • Associated Minerals are erythrite and annabergite which form weathering crusts; also other cobalt and nickel sulfides and arsenides such as cobaltite.
  • Other Characteristics: sometimes irridescent.
  • Notable Occurances include Cobalt, Ontario; Skutterud, Norway; Franklin, New Jersey and other cobalt mines around the world.
  • Best Field Indicators are crystal habit, color, streak, lack of good cleavage and associations.

 

 

 

 

THE MINERAL SMITHSONITE

 


Smithsonite is named for James Smithson, the founder of the Smithsonian Institution. The luster of smithsonite sets it apart from other minerals: it has a silky to pearly luster giving natural specimens a certain play of light across its surface that resembles the fine luster of melted wax glowing under a candle flame. It is easy to wax poetically when discussing smithsonite's unique luster. It is really unusual and captivating and collectors can easily get hooked.

Smithsonite in addition to wonderful luster also has a varied color assortment. The apple green to blue-green color is probably smithsonite's most well known color, but it is its purple to lavender color that is probably its most sought after hue. There also exists attractive yellow, white, tan, brown, blue, orange, peach, colorless, pink and red smithsonite specimens and all of them are a credit to this mineral.

The typical crystal habit of smithsonite is an interesting form called botryoidal. This form has the appearance of grape bunches and is the result of radiating fibrous crystals that form from central attachment points and grow outward and into each other. The result is a rounded, bubbly landscape for which smithsonite is considered the classic example. There are also other habits more typical of Calcite Group minerals including rounded rhombohedrons and scalenohedrons. Most of these come from the famous mines of Tsumeb, Namibia and the Broken Hill Mine in Zambia. The Tsumeb specimens are colored by trace amounts of cobalt and can have some real exotic colors. The Kelly Mine, Magdalena, New Mexico has produced the absolute finest blue-green botryoidal masses of smithsonite. But there are many localities that have or are producing excellent specimens.

Smithsonite has been and is still being used as an important, although rather minor ore of zinc. At Leadville, Colorado the smithsonite deposits were largely overlooked until their profit potential was finally realized. Many other zinc ore minerals may have been originally smithsonite before metamorphism or other altering processes, formed new minerals. Smithsonite forms in dry climates as a weathering product of primary sulfide zinc ores such as sphalerite.

Smithsonite is not easy to confuse with many other minerals. Hemimorphite has a similar botryoidal habit and blue-green color, but the fracture edges of smithsonite's specimens have a plastic-like look while hemimorphite reveals minute, radiating crystals. Prehnite has similar color and habit as well, but is much lighter and harder. Both of these minerals lack the melted wax luster of smithsonite. Its high density, good cleavage, crystal habit, luster, its reaction to hot HCl acid and its high hardness for a carbonate are all quite conclusive for smithsonite to be differentiated from all other minerals. With its lovely luster, many beautiful colors and interesting habits, smithsonite specimens are a source of real pleasure for collectors around the world.

 

PHYSICAL CHARACTERISTICS:

  • Color is commonly apple green, blue-green, lavender, purple, yellow and white as well as tan, brown, blue, orange, peach, colorless, gray, pink and red.
  • Luster is usually pearly to resinous with light play across its surface and sometimes is simply vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is trigonal; bar 3 2/m
  • Crystal Habits include the rhombohedrons and scalenohedrons with generally curved faces. But more commonly is botryoidal or globular.
  • Cleavage is perfect in three directions forming rhombohedrons.
  • Fracture is uneven.
  • Hardness is 4 - 4.5.
  • Specific Gravity is approximately 4.4 (heavy for nonmetallic minerals)
  • Streak is white.
  • Associated Minerals are those found in oxidation zones of zinc sulfide deposits such as hemimorphite, cerussite, wulfenite, limonite, mimetite, dolomite, hydrozincite, aurichalcite, calcite and other carbonate minerals.
  • Other Characteristics: Effervesces slightly with warm hydrochloric (HCl) acid.
  • Noteable Occurrences include Tsumeb, Namibia and the Broken Hill Mine in Zambia; the Kelly Mine, Magdalena, New Mexico; Leadville, Colorado; Utah; Idaho and Arizona, USA; Mexico; Laurion, Greece; Bytom, Poland; Moresnet, Belgium and many other localities.
  • Best Field Indicators are luster, typical botryoidal habit, cleavage, hardness, reaction to hot acids and density.



 

 

THE MINERAL SODALITE

 


Sodalite is a scarce mineral that can be rock forming. Sodalite is named in reference to its sodium content. It is used for carvings and some jewelry pieces. Its light to dark pure blue color is well known in the semi-precious stone trade. Sodalite is a member of the feldspathoid group of minerals. Minerals whose chemistries are close to that of the alkali feldspars but are poor in silica (SiO2) content, are called feldspathoids. As a result or more correctly as a function of the fact, they are found in silica poor rocks containing other silica poor minerals and no quartz. If quartz were present when the melt was crystallizing, it would react with any feldspathoids and form a feldspar.. Localities that have feldspathoids are few but some produce large quantities of sodalite. Sodalite, when not blue, is hard to distinguish from other feldspathoids. It is the only feldspathoid that contains chlorine. Sodalite dissolved in a dilute solution of HNO3 gives a positive chlorine test obtained from some swimming pool test kits.

 

PHYSICAL CHARACTERISTICS:

  • Color is blue, white, gray, or even green.
  • Luster is vitreous or greasy
  • Transparency: Crystals are transparent to translucent, massive specimens are opaque.
  • Crystal System: Isometric; bar 4 3/m
  • Crystal Habits: Dodecahedral crystals have been found, usually massive as a rock forming mineral.
  • Cleavage is poor, in six directions, but rarely seen.
  • Fracture is uneven
  • Hardness is 5.5 - 6.0
  • Specific Gravity is 2.1 - 2.3
  • Streak white
  • Associated Minerals calcite, nepheline, cancrinite and other feldspathoids.
  • Other Characteristics: it is the only feldspathoid to give a positive chlorine test when dissolved in a HNO2 dilute solution.
  • Notable Occurrences include Bancroft, Ontario; Mt. Vesuvius, Italy; Brazil; Ice River area, British Columbia and Maine, USA.
  • Best Field Indicators are color if blue, lack of pyrite association (as in lazurite), hardness and associations.




 

 

THE MINERAL SPANGOLITE

 

  • Chemistry: Cu6Al(SO4)Cl(OH)12 - 3H2O, Hydrated Copper Aluminum Sulfate Chloride Hydroxide.
  • Class: Sulfates.
  • Uses: As a minor ore of copper and as mineral specimens.
  • Specimens

Spangolite is a yet another classic Cornwall mineral although it was first described from a sample that came from the copper districts near Tombstone and/or Bisbee, Arizona, USA. The type locality is in doubt because the original type specimen's origin was unknown, but thought to have originated near Tombstone. Later authors have given strong evidence that the specimen is more likely from Bisbee. A good tale to tell to young collectors about keeping good records. You never know when a mineral specimen will yield a new mineral and it is a shame to have its origin in doubt! Cornwall's discovery was just a few years after the 1890 Arizona discovery.

Spangolite is a beautiful mineral. It has a blue green color that is usually quite attractive. Its aggregate crystal clusters of tabular well formed crystals are very interesting and spangolite even forms small twinned crystals that have a look similar to the head of a double bladed hatchet. Spangolite's typical tabular habit is similar to the arsenate mineral chalcophyllite.

 

PHYSICAL CHARACTERISTICS:

  • Color is blue-green; ranging from dark blue to emerald green.
  • Luster is vitreous.
  • Transparency: Specimens are transparent to translucent.
  • Crystal System is hexagonal; 6mm.
  • Crystal Habits include prismatic to tabular tapering crystals.
  • Cleavage is perfect in one direction (basal).
  • Fracture is conchoidal.
  • Hardness is 3
  • Specific Gravity is approximately 3.1 - 3.2 (average for non-metallic minerals).
  • Streak is light green.
  • Associated Minerals include azurite, cuprite, claringbullite, connellite, paratacamite, atacamite, and chyrsocolla.
  • Notable Occurrences include St. Day, Cornwall, England; Arenas, Sardinia; Larium, Greece; the type locality of either Tombstone or Bisbee, as well as the Copper Queen Mine and the Clifton-Morenci District of Arizona, and the Bingham and Blanchard Mine, Socorro County, New Mexico, USA.
  • Best Field Indicators are crystal habit, color, cleavage, associations and locality.



 

 

THE MINERAL SPERRYLITE

 


Sperrylite is a rare, but economically important mineral. Although not found in very many places around the world, and in all but one of these it is a minor constituent, sperrylite is an important ore of platinum. In fact, besides native platinum, it is the only platinum ore of any significance. Sperrylite is found in abundance only at Sudbury, Ontario where it is mined for its extremely valuable metal.

Sperrylite is a cousin of the much more common and well known mineral, pyrite. Both belong to the Pyrite Group of minerals and share a similar structure and therefore similar crystal habits. They can not be mistaken for each other however since pyrite is brassy yellow and sperrylite is tin white in color.

Pyrite's and sperrylite's structure is analogous to galena's structure with a formula of PbS. Galena though has a higher symmetry. The difference between the two structures is that the single sulfur of galena is replaced by a pair of sulfurs in sperrylite. The sulfur pair are covalently bonded together in essentially an elemental bond. This pair disrupts the four fold symmetry that a single atom of sulfur would have preserved and thus gives sperrylite a lower symmetry than Galena.

 

PHYSICAL CHARACTERISTICS:

  • Color is tin white.
  • Luster is metallic.
  • Transparency: Crystals are opaque.
  • Crystal System is isometric; bar 3 2/m
  • Crystal Habits include usually rounded crystals showing the cube, octahedron or pyritohedron (a dodecahedron with pentagonal faces). Crystals with combinations of these forms are more common. Also massive and reniform.
  • Cleavage is very indistinct (cubic).
  • Fracture is conchoidal.
  • Hardness is 6 - 7
  • Specific Gravity is approximately 10.6 (very heavy even for metallic minerals).
  • Other Characteristics: Brittle, striations on cubic faces caused by crossing of pyritohedron with cube. (note - striations on cube faces also demonstrate sperrylite's lower symmetry).
  • Associated Minerals are chalcopyrite, pyrrhotite and pentlandite.
  • Notable Occurrences include Sudbury, Ontario, Canada and the Bushveld rocks of Transvaal, South Africa.
  • Best Field Indicators are crystal habit, hardness, luster, associations, color and lack of good cleavage.



 

 

THE MINERAL SPESSARTINE

 

Spessartine, like other garnets, forms rounded crystals with 12 rhombic or 24 trapezoidal faces or combinations of these and some other forms. This crystal habit is classic for the garnet minerals. Spessartine is formed in manganese rich metamorphic enviroments and in some granitic pegmatites. Spessartine is somewhat rare but occassionally will accompany other minerals and make a nice accessory mineral to an outstanding mineral specimen.

 

PHYSICAL CHARACTERISTICS:

  • Color is orange, reddish brown, brown, pink and yellow.
  • Luster is vitreous.
  • Transparency crystals are transparent to translucent.
  • Crystal System is isometric; 4/m bar 3 2/m
  • Crystal Habits include the typical rhombic dodecahedron. But more commonly is found as the 24 sided trapezohedron. Combinations of these forms are common and sometimes the rare faces of the hexoctahedron, a 48 sided crystal habit that rarely is seen by itself, can also combine with these other forms making very attractive, complex and multifaceted crystals. Massive and granular occurrences are also seen.
  • Cleavage is absent.
  • Fracture is conchoidal.
  • Hardness is 7
  • Specific Gravity is approximately 4.19 or less (above average for translucent minerals).
  • Streak is white.
  • Associated Minerals are feldspars, quartz, tourmalines, topaz, beryl, rhodonite and other manganese minerals.
  • Other Characteristics: index of refraction is 1.80
  • Notable Occurrences are Pakistan; Madagascar; Brazil and Sri Lanka.
  • Best Field Indicators are crystal habit, color, and hardness.
  •  

 

 

THE MINERAL SPHAEROCOBALTITE

 


Sphaerocobaltite is a beautiful and colorful mineral. It is also known as cobaltocalcite and cobaltian-calcite. However, these names are often used when referring to calcite that has an appreciable amount of cobalt in its structure as an impurity. The result of the presence of the cobalt is that the calcite is colored a pale pink. In pure sphaerocobaltite (most examples contain a small but significant percentage of calcium), the coloring effect is magnified.

The sometimes deep rose-red to pink color is very attractive and unique. It is easy to confuse sphaerocobaltite with two other carbonates; rhodochrosite and stichtite, because all three are described as red to pink minerals. However, side by side the color difference is obvious, as sphaerocobaltite has a more "hot pink" color than the redder pink of rhodochrosite or the more purple-pink of stichtite. Confused? Well, you just need to see them.

Sphaerocobaltite, fortunately, is further distinguished by its occurrences with cobalt bearing veins that have been affected by carbonated waters. It is found as crusts and small crystals in many cobalt ore locations around the world, but it is the mines of Shaba, Zaire that have produced the most outstanding specimens. Some specimens are draped with acicular dark green malachite crusts and the combination makes for a very colorful specimen.

 

PHYSICAL CHARACTERISTICS:

  • Color is red to pink.
  • Luster is vitreous.
  • Transparency crystals are transparent to translucent.
  • Crystal System is trigonal; bar 3 2/m
  • Crystal Habits include rhombohedrons and scalahedrons, but large crystals are rare. Often, any large crystals are sphaerocobaltite intergrown with calcite, coloring the whole crystal pink. Also botryoidal, globular, stalactitic and as crusts.
  • Cleavage is perfect in three directions, forming rhombohedrons.
  • Fracture is uneven.
  • Hardness is 4.
  • Specific Gravity is approximately 4.2 (above average for translucent minerals).
  • Streak is pale pink.
  • Associated Minerals are calcite, malachite, cobaltite and dolomite.
  • Other Characteristics: red or pink and white banding in massive forms and effervesces easily with dilute acids.
  • Notable Occurrences include Shaba, Zaire; Saxony Germany and from other secondary cobalt ore locations.
  • Best Field Indicators are color, crystal habit, reaction to acid, associations with cobalt ore deposits, and cleavage.

 

 

 

   

THE MINERAL SPHALERITE

 


Sphalerite (which is also known as Blende), is an important ore of zinc and can make a rather attractive cabinet specimen as well. It can have excellent luster and associates with many beautifully colored minerals making it one of the best enhancers of many fine mineral specimens.

Sphalerite is one of the very few minerals that has a total of six directions of cleavage. If all of them were to be perfectly cleaved on a single crystal it would form a rhombic dodecahedron. Identifying all six directions in a single cleaved crystal is quite difficult due to the multiple twinning and the many directions. Only the fact that there is abundant cleavage at different directions can easily be seen in most cleaved specimens.

Sphalerite can be difficult to identify because of its variable luster, color, abundant but obscured cleavage and crystal habits. So difficult was sphalerite for miners to distinguish from more valuable minerals such as galena, acanthite and tetrahedrite, that they named it sphalerite which is Greek for treacherous rock and blende is German for blind or deceiving.

The luster of sphalerite is truly its best attribute. It typically has a nice adamantine luster that really sparkles owing to its unusually high index of refraction and a fire greater than diamond's. Specimens of sphalerite are usually adorned with hundreds of small sparkling faces. Groups of faces can be symmetrically oriented into several different directions so that as a particularly gifted specimen is turned with respect to a viewer they are treated to several episodes of multiple and bright flashes. Transparent sphalerite has been cut for gemstones but its cleavage and softness limit its use as a gemstone to collectors only.

The twinning of sphalerite is also special. It can form a spinel twin which is a specialty of the mineral spinel. The spinel twin is where a tetrahedral crystal is twisted in the middle so that three points of the tetrahedron are in alignment with the other three points. These crystals are not usually completely developed in sphalerite but the indentations that the twinning causes are usually seen on some crystals in almost every specimen. A twin type for some reason called a "chicken twin" or "hen" forms a sort-of football shaped twin.

Sphalerite is a polymorph with two minerals, wurtzite and matraite. The three are called polymorphs (meaning many shapes) because although they have the same chemistry, (Zn, Fe)S or zinc iron sulfide, they have different structures and therefore different shapes. Sphalerite is by far the more common mineral of the three.
Sphalerite's structure is analogous to the diamond structure. If every other carbon in the diamond structure is replaced by a sulfur atom and the remaining carbons are replaced with either a zinc or an iron atom then basically the mineral is sphalerite.

Sphalerite is by no doubt the most important ore of zinc, an industrially and at times strategically important metal. Other zinc ores include hemimorphite, smithsonite, willemite, franklinite and zincite. Although its importance as an ore of zinc is undisputed, it is a very attractive and a very interesting mineral for collectors as well.

 

PHYSICAL CHARACTERISTICS:

  • Color is typically black but can be brown, yellow, reddish, green, and less commonly white or colorless.
  • Luster is adamantine or resinous or submetallic to earthy in massive forms.
  • Transparency crystals are transparent to translucent.
  • Crystal System is isometric; bar 4 3m
  • Crystal Habits can be complicated with the rhombic dodecahedron, tetrahedron and combinations of these having cubic and tristetrahedron faces giving the crystals multiple faces of often indistinct forms. To add more confusion to the indistinct crystals, twinning is common and sometimes pervasive. Massive forms are common and can be granular, earthy, botryoidal, concretionary and fibrous. An aggregate of botryoidal crusts with layers of wurtzite and galena is called "Schalenblende" is sometimes cut and polished as an ornamental stone.
  • Cleavage is perfect in six directions forming dodecahedrons.
  • Fracture is conchoidal, but rarely seen because of frequent cleavage.
  • Hardness is 3.5-4
  • Specific Gravity is approximately 4.0 (heavier than average, but light when compared to most metallic minerals)
  • Streak is yellow to light brown (unusually light colored for a normally dark mineral).
  • Other Characteristics: Striations on tetrahedral faces, triboluminescent (meaning it may glow if crushed), an index of refraction of 2.37 - 2.42, a dispersion (fire) of 0.156 and finally sphalerite is pyroelectric (meaning that it forms a slight electrical charge when heated or cooled).
  • Associated Minerals almost always include galena, pyrite, fluorite, chalcopyrite, quartz, calcite, magnetite, pyrrhotite and many others.
  • Notable Occurrences include Tri state area near Joplin, Missouri; Rosiclare, Illinois; Elmwood, Tennessee, USA; Broken Hill, Australia; Italy; Spain; Burma; Peru; Morocco; Germany and England.



        

THE MINERAL SPHENE

 

  • Chemistry: CaTiSiO5, Calcium Titanium Silicate
  • Class: Silicates
  • Subclass: Nesosilicates
  • Uses: Mineral specimens, source of TiO2 (a pigment) and as a gemstone.
  • Specimens

Sphene is named from the greek word for wedge, because of its typical wedge shaped crystal habit. It is also alternatively called titanite for its titanium content. Spene can be cut as gems although it is considered a rarity on the gem market. It brings to the table a fire greater than diamond and unique color shades. However its softness limits its desirability as a gemstone. Twinning is common in sphene and forms a classic twin shape that is found mostly in Pakistan. The twin is shaped like a deflated, caved-in football, only with flatter surfaces. Spene can form nice crystals and can make a lovely addition to the collection of a collector who appreciates different crystal forms.

 

PHYSICAL CHARACTERISTICS:

  • Color is green, yellow, white, brown or black.
  • Luster is adamantine.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System: Monoclinic; 2/m
  • Crystal Habits include elongated wedges that form tabular or platy crystals. Some crystals are not so elongated and can have a trigonal appearance similar to a flattened rhombohedron. Twinning is common and produces a twin that is shaped like a deflatted, caved-in football, only with flatter surfaces.
  • Cleavage is indistinct in two directions
  • Fracture is conchoidal
  • Hardness is 5 - 5.5
  • Specific Gravity is 3.3 - 3.6
  • Streak is white.
  • Associated Minerals are chlorite, anatase, calcite, quartz, zircon and feldspars.
  • Other Characteristics: Pleochroic if strongly colored.
  • Notable Occurances include Gilget, Pakistan; Mt Vesuvius, Italy; Kola Penn., Russia; Ontario, Canada and New York and California, USA.
  • Best Field Indicators are crystal habit, luster, hardness, twinning if present and color.


         

 THE MINERAL SPINEL

 


Spinel is a very attractive and historically important gemstone mineral. Its typical red color, although pinker, rivals the color of ruby. In fact, many rubies, of notable fame belonging to crown jewel collections, were found to actually be spinels. Perhaps the greatest mistake is the Black Prince's Ruby set in the British Imperial State Crown. Whether these mistakes were accidents or clever substitutions of precious rubies for the less valuable spinels by risk taking jewelers, history is unclear. The misidentification is meaningless in terms of the value of these gems for even spinel carries a considerable amount of worth and these stones are priceless based on their history, let alone their carat weight and pedigree.


Today, expensive rubies are still substituted for by spinel in much the same way a diamond is substituted by cubic zirconia. Not to commit a fraud or theft but to prevent one. Spinel may take the place of a ruby that would have been displayed in public by an owner who is insecure about the rubies safety. The spinel probably is still valuable but better to lose a $100,000 dollar spinel than a $1 million dollar ruby!

Spinel and ruby are chemically similar. Spinel is magnesium aluminum oxide and ruby is aluminum oxide. This is probably why the two are similar in a few properties. Not suprisingly, the red coloring agent in both gems is the same element, chromium. Spinel and Ruby also have similar luster (refractive index), density and hardness. Although ruby is considerably harder (9) than spinel, spinel's hardness (7.5 - 8) still makes it one of the hardest minerals in nature.

Spinel may be the poorer cousin of ruby, but its pinker color and other qualities make it attractive in its own right. Spinel typically forms in well formed octahedrons. But it is famous for a type of twinning that bears its name, the Spinel Twin Law. Spinel Law twinning is also found in other isometric minerals such as diamond, galena, cristobalite, magnetite, franklinite and other members of the spinel group. This type of twinning produces a twin plane that is parallel to one of the octahedral faces. The plane acts as a mirror plane and produces a left and right side that are mirror images of each other. This may not sound all that spectacular for a very symmetrical mineral like spinel which is loaded with mirror planes. However this mirror plane is not parallel to any of the others and actually lowers the symmetry of the crystal (only in appearances though).

A good description of the twin is hard to explain, but here it goes. The plane falls (of course) in the center of the crystal, dividing it in half. The two octahedron faces parallel to the twin plane are equilateral triangles. Each point of the triangles is doubled across the twin plane with an indentation between them. The crystal looks like it has trigonal symmetry, but the three indentations are a clue that this crystal is a twin. Twins of spinel are rare, but their popularity makes them readily available on the market.

 

PHYSICAL CHARACTERISTICS:

  • Color is red, green, blue, purple, brown, and black; but red is by far the more common color.
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent and sometimes nearly opaque.
  • Crystal System: Isometric; 4/m bar 3 2/m
  • Crystal Habits include the typical octahedron, but can be found as dodecahedrons and combinations of other isometric forms. Also as rounded grains in alluvial placer deposits.
  • Cleavage: None
  • Fracture is conchoidal.
  • Hardness is 7.5-8.0
  • Specific Gravity is 3.6-4.0
  • Streak is white.
  • Other Characteristics: index of refraction is approximately 1.71 - 1.76 and rutile inclusions may produce six or four rayed stars or asterisms.
  • Associated Minerals include calcite, dolomite, corundum and garnets.
  • Notable Occurrences include Burma, Sri Lanka, Brazil and Afghanistan.
  • Best Field Indicators are twinned crystals if present, color, hardness, density and locality.


 

THE MINERAL SPODUMENE

 

Also see variety specimens:

Spodumene is a rock forming mineral in granites and pegmatites that bear other lithium minerals. Spodumene is a relatively new mineral to science, being discovered in the last three centuries and gem varieties have only been discovered in the last 120 years. Transparent deeply colored spodumene has two varieties called Kunzite and Hiddenite. Kunzite is the more common of the two and is known by most gemstone collectors and fanciers. It is a lovely pink to lilac color that is unique in the gem kingdom. Hiddenite comes North Carolina and is not well known or abundant. It has an usual green color that is unlike either peridot or emerald. Spodumene is strongly pleochroic and therefore a gem cutter must take care to orient the stone in the best position for the deepest color. Spodumene's cleavage, parting and fracture also make it a challenge for any gem cutter.

 

PHYSICAL CHARACTERISTICS:

  • Color is white, colorless, gray, pink, lilac, violet, yellow and green.
  • Luster is vitreous.
  • Transparency crystals are transparent to translucent.
  • Crystal System is monoclinic; 2/m
  • Crystal Habits include prismatic, generally flattened and elongated crystals. The termination is usually the two faces of a dome or rounded, curved and faces indisernable. Crystal faces are often pitted and rough. Some crystals of spodumene have been found in record large crystals of more than 12 meters long.
  • Cleavage is perfect in two direction at close to right angles and a parting direction that breaks diagonally transect one of the cleavage angles and is parallel to the typical flattening of the crystals.
  • Fracture is splintery due to the cleavage and parting.
  • Hardness is 6.5 - 7
  • Specific Gravity is approximately 3.2 (slightly above average)
  • Streak is white.
  • Associated Minerals are lepidolite, plagioclase feldspars, quartz, tourmaline and topaz.
  • Other Characteristics: index of refraction is 1.66, prism faces are deeply striated lengthwise and clear colorful varieties show strong pleochroic color intensity variation when a crystal is viewed from the top or bottom then from other directions.
  • Notable Occurrences include California, North Carolina and South Dakota, USA; Afganistan; Pakistan; Brazil and Madagascar.
  • Best Field Indicators are crystal habit, striated prisms, color, fracture and cleavage.



 

   

THE MINERAL STAUROLITE

 


Staurolite is a common metamorphic mineral that is useful to geologists to determine the degree of metamorphism. Staurolite is famous for its twinned crystals that form into the shape of a cross. Its name comes from the greek for cross. The twin is a classic penetration twin where it appears as if two crystals grew into and out of each other. It actually forms two twin types; one that is nearly 90 degrees and one that is nearly 60 degrees. The 60 degree type is more common but the 90 degree type is the most sought after. It was associated with Christianity as a symbol for the cross and as a good luck charm. It has been given the names "Fairy Stone" or Fairy Cross". Some scarcer specimens show both twin forms and can look like a blunt six rayed star.

 

 

PHYSICAL CHARACTERISTICS:

  • Color is reddish-brown, brown, and black.
  • Luster is vitreous to resinous to dull.
  • Transparency crystals are translucent to opaque.
  • Crystal System monoclinic; 2/m
  • Crystal Habits: the typical crystal are prismatic or tabular. Some crystals can have a psuedo-hexagonal cross-section but most are flattened into a more diamond shaped cross-section with two of the four points truncated. Twinning is seen in about 35% of the specimens encountered in nature. Twins are cross (+) or X-shaped and can be both at the same time. Crystals sometimes grown onto kyanite crystals.
  • Cleavage poor, in one direction.
  • Fracture is uneven to conchoidal
  • Hardness is 7-7.5
  • Specific Gravity is 3.7-3.8
  • Streak white
  • Associated Minerals include almandine, micas, kyanite and other metamorphic minerals.
  • Other Characteristics:
  • Notable Occurances Ducktown Tennessee, Georgia, Virginia and Montana, USA; Brazil; Scotland, Italy and France.
  • Best Field Indicators are color, associations, twinning and crystal habit.



 

    

 THE MINERAL STELLERITE

 


Stellerite is the rarer cousin of the much more common zeolite stilbite, NaCa2 Al5 Si13 O36 -14H2 O. Stellerite differs from stilbite because of the substitution of aluminum for silicon in the framework stucture. Stilbite has an extra aluminum, at +3, for every seven silicons, at +4, and therefore requires a sodium, at +1, to balance the chemical equation.

Like stilbite, stellerite crystals can aggregate together to form a structure resembling wheat sheafs. This hourglass structure looks like several crystals stacked parallel to each other with the tops and bottoms of this structure fanning out while the middle remains thin. More commonly stellerite is found in rounded radiating clusters or as single crystals. Stellerite and stilbite are almost identical is certain situations. Stellerite however appears more transparent and is usually uncolored.

Stellerite's structure has a typical zeolite openness about it that allows large ions and molecules to reside and actually move around inside the overall framework. The structure contains open channels that allow water and large ions to travel into and out of the crystal structure. The size of these channels controls the size of the molecules or ions and therefore a zeolite like stellerite can act as a chemical sieve. Stellerite's structure contains rings of alumino-silicate tetrahedrons oriented in one direction and this produces the prominant pinacoid faces, the perfect cleavage and the unique luster on those faces. Stellerite can form nice crystals inside the petrified bubbles (called vesicles) of volcanic rocks that have undergone a small amount of metamorphism.

 

PHYSICAL CHARACTERISTICS:

  • Color is colorless or white and rarely tinted pink, yellow or brown.
  • Luster is vitreous to pearly especially on the prominant pinacoid and cleavage surfaces.
  • Transparency: crystals are transparent to less commonly translucent.
  • Crystal System is monoclinic; 2/m
  • Crystal Habits include radiating nodules and platy often thin crystals that can aggregate together into a wheat sheaflike structure. The prominant pinacoid is sometimes but rarely modified by other pinacoid and prism faces.
  • Cleavage is perfect in one direction parallel to the prominant pinacoid.
  • Fracture is uneven.
  • Hardness is 3.5.
  • Specific Gravity is approximately 2.2 (very light)
  • Streak is white.
  • Associated Minerals are quartz, calcite, apophyllite, babingtonite, heulandite, stilbite, natrolite and other zeolites.
  • Notable Occurrences include Poona, India; New Jersey and Nova Scotia.
  • Best Field Indicators are crystal habit, luster, density and associations.

 

        

 THE MINERAL STEPHANITE

 

  • Chemistry: Ag5SbS4, Silver Antimony Sulfide
  • Class: Sulfides
  • Subclass: Sulfosalts
  • Uses: An ore of silver and as mineral specimens.
  • Specimens

Stephanite is an uncommon silver bearing mineral that is named after a onetime Archduke of Austria, Victor Stephan. Although not a well known ore of silver, it is never-the-less a locally important ore in some mines. Stephanite typically forms nicely shaped crystals that are tabular to short prismatic. Its crystals can have a pseudohexagonal outline making them look like crystals of polybasite, a closely related mineral. Stephanite lacks polybasite's rhombic striations on its pinacoidal faces, good cleavage and the red flashes.

 

PHYSICAL CHARACTERISTICS:

  • Color is an iron black to dark gray.
  • Luster is metallic.
  • Transparency: Crystals are opaque.
  • Crystal System: Orthorhombic; 2 m m
  • Crystal Habits include tabular or short prismatic crystals that are dominated by prominent pinacoidal faces. Crystals are sometimes intergrown and form pseudohexagonal plates. Also as disseminated grains and massive.
  • Cleavage is poor in two directions.
  • Fracture is conchoidal to uneven.
  • Hardness is 2 - 2.5
  • Specific Gravity is approximately 6.2 - 6.3 (heavy even for metallic minerals)
  • Streak is a black.
  • Other Characteristics: Dark coating can often form after prolonged exposure to light (can be removed by ultrasonic treatment) and crystals tend to be striated perpendicular to the prominent pinacoids.
  • Associated Minerals include silver, proustite, pyrargyrite, polybasite, sphalerite, quartz, barite, calcite, pyrite, fluorite, galena, tetrahedrite , acanthite and other silver sulfide minerals.
  • Notable Occurrences include Sonora, Mexico; Freiberg, Saxony, Germany; Colorado, California and Comstock, Nevada, USA; Atacama, Chile; Cobalt, Ontario, Canada; Cornwall, England and Bolivia.
  • Best Field Indicators are good crystal habit, density, softness, association with other silver sulfosalts and lack of cleavage.



 

   

THE MINERAL STIBARSEN

 


Stibarsen is named for its chemistry and is an unusual Elements Class mineral. The "stib" in the name is for the Latin word for antimony, stibium; from where antimony gets its symbol, Sb. The closely related elements antimony and arsenic are semi-metals meaning they share some properties with metals such as metallic luster and at least some electrical conductivity; but differ in other characteristics such as a tendency to bond with covalent bonds instead of with metallic bonds. Stibarsen, which has also been known as allemontite, is classified as an element despite the fact, that in chemical reality, it is a compound! The reason for this is that the elemental bonds that exist between antimony and arsenic are very similar to the bonds of other non-metallic elemental minerals such as diamond or sulfur. If the arsenic or antimony were bonded to a true metal instead of a semi-metal then the mineral would be classified in the Sulfides Class instead of the Native Elements Class.

Stibarsen is a very rare mineral, but is a joy to see. It has a bright silvery color and a good botryoidal habit. The effect presents to the viewer a mass of what appears to be a highly polished rounded mass of high grade silver!

 

PHYSICAL CHARACTERISTICS:

  • Color is silver, white, reddish-white to gray.
  • Luster is bright metallic.
  • Transparency: Specimens are opaque.
  • Crystal System is trigonal.
  • Crystal Habits is limited to botryoidal masses.
  • Cleavage is perfect.
  • Fracture is hackly.
  • Hardness is 3 - 4
  • Specific Gravity is 6.0 - 6.3 (above average for a metallic mineral)
  • Streak is gray black.
  • Associated Minerals include apatite, beryl, microcline, micas and other pegmatite minerals.
  • Notable Occurrences are limited to the type locality at the quarry at Varutrask, Vasterbotten, Sweden and also at Trebsco, Bohemia; Rio Moctezuma, Sonora, Mexico.
  • Best Field Indicator is crystal habit, color, luster, locality and density.



 

 

THE MINERAL STIBICONITE

 

  • Chemistry: Sb3O6(OH) , Antimony Oxide Hydroxide
  • Class: Oxides
  • Group: Stibiconite
  • Uses: mineral specimens and a very minor ore of antimony
  • Specimens

Stibiconite is a rather rare mineral, but is known among collectors for its first class pseudomorphs. A pseudomorph is an atom by atom replacement of one mineral's chemistry to form another completely different mineral. The process leaves the crystal shape of the lost mineral intact. pseudomorph means false (psuedo) shape (morph). In the case of stibiconite, the mineral that is lost is stibnite, Sb2S3. Stibnites sword-like crystals arranged in radiating clusters are truly works of natural art. A pseudomorph of stibiconite can perfectly match the sword-like shape of stibnite's crystals. It can do this because the process is done slowly, allowing the oxygens to replace the sulfurs essntially, one atom at a time. However, stibiconite lacks the metallic luster or steel gray color of stibnite. If two classic specimens of the minerals are put side by side the color and luster contrasts along with the similarity of the crystal shapes would simply fasinate the onlooker.

As might be guessed, stibiconite forms in the oxidation zone of antimony sulfides. The oxygens oxidize a portion of the antimonies (Sb) from +3 (as in stibnite) to +5. The two different valences occupy different sites in the structure of the mineral, since the size of the atoms diminsh greatly when reduced in charge. To represent this, the formula could be written as so, Sb(+3)Sb(+5)2O6(OH). This formula more closely fits the general formula for the Stibiconite Group, M1 - 2X2O6(O, OH, F).

Some of the finest stibiconites, producing wonderful pseudomorphs, occur in a few new antimony mines that have yet to produce any unaltered stibnite clusters. It is hoped that these mines will break through the oxidation layers into some pockets of amazingly stunning stibnite specimens. These stibiconites, although in their own right magnificent, only tease the stibnite collectors as to what once was there.

 

PHYSICAL CHARACTERISTICS:

  • Color is white or gray but usually tinted brown or yellow.
  • Luster is earthy.
  • Transparency crystals are opaque.
  • Crystal System is isometric, possibly.
  • Crystal Habits: include the earthy masses and crust but well known for its stibnite pseudomorphs showing a sword-like bladed habit, singular or in radiating clusters.
  • Cleavage none
  • Fracture is earthy
  • Hardness is 4 - 5.5
  • Specific Gravity is 3.5 - 5.9 (above average to heavy)
  • Streak is white.
  • Associated Minerals include stibnite, valentinite, and other antimony oxides.
  • Other Characteristics: a white coating may appear on specimens with time (don't try to remove).
  • Notable Occurrences include Goldkronach, Germany; Wolfe County, Quebec; San Luis Potosi, Mexico; Nevada, USA and Huaras, Peru.
  • Best Field Indicators are stibnite-like crystals, color, luster, hardness and density.



 

    

THE MINERAL STIBNITE

 

  • Chemistry: Sb2S3, Antimony Sulfide
  • Class: Sulfides
  • Uses: An ore of antimony and as mineral specimens.
  • Specimens

Stibnite is a classic mineral species with fine crystal clusters and long curved crystals being the pride of many collectors. The slender curved metallic blades of stibnite can resemble arabian swords. The curving of the long bladed crystals is due to twinning where one twin plane bends the crystal one direction and another twin plane bends it in the other direction. This can occur numerous times down the length of one crystal. Stibnite's crystal clusters are admired for their distinctive look with dozens of accicular or bladed crystals jutting out in many divergent directions.

 

PHYSICAL CHARACTERISTICS:

  • Color is steel gray to silver.
  • Luster is metallic.
  • Transparency crystals are opaque.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include bladed or acicular crystals often bent or curved due to twinning, also granular and massive.
  • Cleavage is perfect in the lengthwise direction.
  • Fracture is irregular.
  • Hardness is 2
  • Specific Gravity is approximately 4.6+ (average for metallic minerals)
  • Streak is a dark gray.
  • Other Characteristics: striated lengthwise sometimes deeply, luster brighter on cleavage surfaces and crystals slightly flexible.
  • Associated Minerals include quartz, calcite, gold, arsenopyrite and other sulfides.
  • Notable Occurrences include Hunan province, China; Japan; Germany; Brazil; Peru and South Africa.
  • Best Field Indicators are crystal habit, softness and flexibility.



 

   

THE MINERAL STICHTITE

 

  • Chemistry: Mg6Cr2CO3(OH)16-4H2O, Hydrated Magnesium Chromium Carbonate Hydroxide
  • Class: Carbonates
  • Group: Hydrotalcite
  • Uses: Very minor ore of chromium, as a mineral specimen and ornamental stone.
  • Specimens

Stichtite is a rare and unusual carbonate. It forms in mostly compact masses or micaceous aggregates and is in stark contrast to the majority of carbonates that form well shaped, large and abundant crystals. Its most common locality is near Dundas on the Island of Tasmania and in fact almost all specimens sold in rock shops and from mineral dealers have Dundas listed as the source. Stichtite has a some what dull purple-ish pink to purple-ish rose-red color. Its color, although similar in description to the other rose-red carbonates, it is actually distinctive in its own right when viewed together with the other pink carbonates. Rhodochrosite is much more redder and has white bands, sphaerocobaltite is more pinkish and stichtite is more purplish. Also adding to the distinction is the fact that the other two carbonates are more crystallized and glassy and stichtite comes from only a very few sources. Massive green serpentine is usually associated with stichtite and this green and purple-ish pink combination can make for an attractive specimen or an ornamental stone carving.

 

PHYSICAL CHARACTERISTICS:

  • Color is a purple-ish rose pink.
  • Luster is waxy or greasy.
  • Transparency: Crystals are translucent.
  • Crystal System is trigonal.
  • Crystal Habits include mostly massive forms that are compact, micaceous or lamellar aggregates.
  • Cleavage is perfect in one direction..
  • Fracture is uneven to flaky.
  • Hardness is 1.5 - 2
  • Specific Gravity is approximately 2.1 (well below average)
  • Streak is white to shades of pink or lilac.
  • Associated Minerals are serpentine and chromite.
  • Notable Occurrences include Dundas, Tasmania, Australia; Black Lake, Quebec, Ontario and South Africa.
  • Best Field Indicators are color, habit, locality and associations.



 

       

THE MINERAL STILBITE

 


Stilbite is a common and perhaps the most popular zeolite mineral for collectors. Stilbite crystals can aggregate together to form a structure resembling wheat sheafs. This hourglass structure looks like several crystals stacked parallel to each other with the tops and bottoms of this structure fanning out while the middle remains thin. Stilbite's hallmark crystal habit is unique to stilbite and a rarer but related zeolite called stellerite. Whether in the wheat sheafs or not, stilbite can be a hansome specimen with its pearly luster and often colorful pink tints. Stilbite commonly forms nice crystals inside the petrified bubbles (called vesicles) of volcanic rocks that have undergone a small amount of metamorphism.

Stilbite's structure has a typical zeolite openness about it that allows large ions and molecules to reside and actually move around inside the overall framework. The structure contains open channels that allow water and large ions to travel into and out of the crystal structure. The size of these channels controls the size of the molecules or ions and therefore a zeolite like stilbite can act as a chemical sieve. Stilbite's structure contains rings of alumino-silicate tetrahedrons oriented in one direction and this produces the prominant pinacoid faces, the perfect cleavage and the unique luster on those faces.

 

PHYSICAL CHARACTERISTICS:

  • Color is pink or white; also tinted yellow and red.
  • Luster is vitreous to pearly especially on the prominant pinacoid and cleavage surfaces.
  • Transparency: crystals are transparent to mostly translucent.
  • Crystal System is monoclinic; 2/m
  • Crystal Habits include platy often thin crystals that can aggregate together into a wheat sheaflike structure. The prominant pinacoid is sometimes but rarely modified by other pinacoid and prism faces. Cruciform (cross-like) twins can also be found. Also forms radiating nodules.
  • Cleavage is perfect in one direction parallel to the prominant pinacoid.
  • Fracture is uneven.
  • Hardness is 3.5 - 4.
  • Specific Gravity is approximately 2.2 (very light)
  • Streak is white.
  • Associated Minerals are quartz, calcite, babingtonite, apophyllite, heulandite, natrolite and other zeolites.
  • Notable Occurrences include Poona, India; Scotland; Iceland; New Jersey and Nova Scotia, Canada.
  • Best Field Indicators are crystal habit, luster, density and associations.

 

 

 

 

THE MINERAL STISHOVITE

 


Stishovite is a polymorph of quartz and the other members of the quartz group, meaning that it is composed of the same chemistry but has a different structure. The structure of stishovite is isostructural with the titanium oxide rutile and all the other minerals of the Rutile Group.

Well formed crystals are very rare as stishovite does not get much time to form crystal faces. It forms quickly at very high pressures but not necessarily at high temperatures. 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 stishovite to be found in nature were identified. Stishovite was actually first synthesized in 1961 before the discovery at Meteor Crater. Now the presence of stishovite is diagnostic evidence of a meteor impact when craters of unknown origin are examined.

Stishovite's basic structural unit is an SiO6 octahedron. This is a much more compact arrangement than the SiO4 tetrahedron of quartz and the other Quartz Group members. Because of this compactness stishovite is the densest member of the Quartz Group and has the highest index of refraction. Comparing stishovite's density and index of refraction to that of quartz's, 4.28 to 2.65 and 1.81 to 1.55 respectively, it is hard to believe that they are both composed of the same elements and in the same proportions.

Stishovite's structure is made of parallel chains of single octahedrons composed of a silicon ion surrounded by six oxygens. It is the parallel chain structure that produces the prismatic crystal habit typical of the Rutile Group. The octahedron chains are arranged with the octahedrons on their "sides" and sharing opposing edges with other octahedrons. The four fold symmetry is the result of the square void created between the chains.

Stishovite is classified as an oxide instead of a silicate like quartz because the structure of stishovite is identical to other oxide minerals. Quartz's structure is the foundation of many tectosilicate minerals and therefore the similarity of quartz's structure to other silicates is justification for its classification, although many mineralogists classify quartz as an oxide.
Stishovite is only metastable at normal surface pressures; 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 so slow a 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 tetragonal; 4/m 2/m 2/m
  • Crystal Habit: Well formed crystals are nonexistent, only found as tiny grains in rocks surrounding meteorite craters.
  • Cleavage is good in two directions forming prisms, poor in a third (basal).
  • Fracture is conchoidal to uneven.
  • Hardness is probably near 6.5.
  • Specific Gravity is 4.28+ (heavy for translucent minerals)
  • Streak is clear.
  • Other Characteristics: refractive index is approximately 1.81.
  • Associated Minerals include other minerals found almost exclusively at meteorite craters such as coesite and iron.
  • Notable Occurrences include Canyon Diablo, Meteor Crater, Arizona, USA and other meteorite craters around the world.
  • Best Field Indicators are environment of formation (meteorite craters), density, cleavage and index of refraction.

 

 

 

 

     

THE MINERAL STRENGITE

 

  • Chemistry: FePO4-2H2O, Hydrated Iron Phosphate
  • Class: Phosphates
  • Group: Variscite
  • Uses: As mineral specimens and limited ornamental stone uses.
  • Specimens

Strengite is an attractive and much sought after rare phosphate mineral. It is found in some very nice colors such as pink and violet red and has a nice vitreous luster. Its habits are somewhat variable but the most beautiful habits include the sphericule nodules and botryoidal masses. It is often associated with other phosphates including the rare and attractive green rockbridgeite. Rockbridgeite forms similar spherical nodules and the two together provide for an interesting specimen with multicolored balls attached to a host rock.

Strengite forms as an alteration product of primary phosphate minerals such as triphylite. Strengite will occur if the oxidation conditions are high enough to oxidize the iron of triphylite from a ferrous (+2) state to the ferric (+3) state as is needed for strengite. The presence of strengite is therefore an indicator of the how much oxidation the rock has under gone.

Another interesting occurrence of strengite is found in some caves whose host rocks contain minerals rich in iron. The alteration to strengite involves the reaction of these minerals with bat guano, or droppings. The phosphorus needed to form strengite is provided from the bat guano. The resulting "minerals" are, in a strick sense, not minerals since they indirectly originated from an organic source, bats.

Strengite forms a series with the more common mineral variscite, AlPO4-2H2O. A series is where different minerals will easily allow certain atoms to freely substitute for each other. In this case iron and aluminum can substitute for each other in variscite and strengite without any disturbance of the crystal structure. Usually the two minerals are fairly pure in nature, but some nearly intermediate specimens have been found.

Strengite is a beautiful mineral and is hard to find on the mineral markets. The best samples are usually small and micromounts are seemingly more available than cabinet samples. Once a specimen is obtained, it will no doubt become a real treasure for the owner.

 

 

PHYSICAL CHARACTERISTICS:

  • Color is colorless or white, but more commonly pink to violet red.
  • Luster is vitreous.
  • Transparency: Specimens are transparent to translucent.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include spherical nodules, rosette aggregates, botryoidal masses, tabular to pseudo-octahedral crystals and crusts.
  • Cleavage is good in one direction, poor in another.
  • Fracture is conchoidal.
  • Hardness is variable from 3 - 4.
  • Specific Gravity is approximately 2.87 (average)
  • Streak is white.
  • Associated Minerals are limonite, heterosite, rockbridgeite, variscite, phosphosiderite, strunzite, beraunite, triphylite and many other secondary phosphate minerals.
  • Notable Occurrences include Rio Grande de Norte, Brazil; Bull Moose Mine, Custer, South Dakota, Indian Mountain, Alabama and San Diego Co., California, USA; Svappavaara, Sweden; Eleonore Mine, Germany and Mangualde, Portugal.
  • Best Field Indicators are color, habit, associations and luster.



 

          

STRONTIANITE

 


Strontianite is a rare carbonate mineral and one of only a few strontium minerals. Crystals are rarer than the massive forms, and so are usually sold as specimens. Typical specimens have spiky, minute crystals in radiating aggregates or tufts. However, it also forms pseudohexagonal twins similar to aragonite's famous twin. It was mined for a while in Germany for strontium, an element used as a coloring agent of fireworks and other applications.

 

PHYSICAL CHARACTERISTICS:

  • Color is white, colorless, gray, yellowish or greenish.
  • Luster is vitreous to greasy.
  • Transparency crystals are transparent to translucent.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include compact, granular, concretionary and massive forms. Crystals are uncommon and are usually pointed and nearly acicular in radiating clusters or tufts. Also forms a psuedo-hexagonal trilling twin is similar to, but is far rarer than aragonite's famous twin.
  • Hardness is 3.5-4
  • Specific Gravity is 3.7+ (above average for transparent minerals)
  • Cleavage is notable in one direction and poor in another.
  • Fracture is subconchoidal to uneven.
  • Streak is white.
  • Other Characteristics: effervesces in only warm HCl solutions or when powdered in cold HCl.
  • Associated Minerals include fluorite, celestite, galena, calcite and aragonite.
  • Notable Occurrences include Strontian, Scotland; San Bernito Co, California and Cave-in-rock, Illinois, USA; Austria and Germany.
  • Best Field Indicators are crystal habits, reaction to acid and density.

The Mineral STRUNZITE

  • Chemistry: MnFe2(PO4)2(OH)2 - 6H2O, Hydrated Manganese Iron Phosphate Hydroxide.
  • Class: Phosphates
  • Uses: Only as mineral specimens.
  • Specimens
Strunzite forms wonderful yellow acicular crystals that form sprays of radiating crystals. It is one of the rare phosphate minerals that comes from classic mineral localities such as Hagendorf, Germany and the Palermo Mine in New Hampshire. It is closely related to the mineral laueite. A casual look at laueite's formula, MnFe2(PO4)2(OH)2 - 8H2O, might lead you to think its the same as strunzite's. But a closer inspection reveals the only difference being two more water molecules in laueite's formula. Those two water molecules make a difference in the structure and a difference in the crystal habit of the two minerals. Laueite forms tabular crystals in contrast to strunzite's acicular or hair-like crystals.

 

PHYSICAL CHARACTERISTICS:

  • Color is bright straw yellow to brown-yellow or brown.
  • Luster is vitreous to silky.
  • Transparency: Specimens are translucent to transparent.
  • Crystal System is triclinic (pseudo-monoclinic).
  • Crystal Habits include acicular to fibrous crystals in radiating sprays and in fibrous crusts.
  • Cleavage is absent.
  • Fracture is uneven.
  • Hardness is 3
  • Specific Gravity is approximately 2.5 - 2.6 (average).
  • Streak is white.
  • Associated Minerals include limonite, triphylite, rockbridgeite, beraunite, laueite and other phosphate minerals.
  • Notable Occurrences includes Hagendorf, Germany; Palermo Mine, New Hampshire and the Black Hills region of South Dakota USA.
  • Best Field Indicators are color, locality, crystal habit, associations and lack of cleavage.

 

 

 

 

 

    

THE MINERAL STURMANITE

 

  • Chemistry: Ca6(Fe, Al, Mn)2(SO4)2(B(OH)4)(OH)12 - 26H2O, Hydrated Calcium Iron Aluminum Manganese Sulfate Tetrahydroxoborate Hydroxide.
  • Class: Sulfates
  • Group: Ettringite
  • Uses: Only as mineral specimens.
  • Specimens

Sturmanite is a rare, attractive and interesting mineral for collectors. It has a very bright yellow color and a nice luster. Sturmanite also forms well shaped crystals. It will commonly form classic hexagonal prisms that are topped by a hexagonal pyramid, which in turn is often truncated by the flat face of a pinacoid. Sturmanite forms as a precipitate from hydrothermal solutions.

Its chemistry is really interesting. Compared with its close cousin, ettringite, Ca6Al2(SO4)3 (OH)12 - 26H2O, one of the sulfate ion groups has been replaced by the rare ion group, (for lack of a shorter term) tetrahydroxoborate, B(OH)4 with a negative one charge. In addition, four out of every five atoms in this mineral is either a part of a water molecule or an hydroxide and that does not count the hydroxides in the B(OH)4 ion group. It's almost all water! This fact is reflected in its very low specific gravity of only 1.8+, that's less than twice the specific gravity of water.

Some mineral references will list sturmanite's chemistry as Ca6Fe2(SO4)2(B(OH)4)(OH)12 - 26H2O. This formula is written without the manganese and aluminum which do substitute for the iron to an appreciable extent.

It is difficult under ordinary means to distinguish ettringite from sturmanite. Both are members of the Ettringite Group and have similar crystal habit, density, luster and will often share the same bright yellow color.

 

 

 

 

 

 

 

PHYSICAL CHARACTERISTICS:

  • Color is a bright yellow.
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is trigonal; bar 3 2/m.
  • Crystal Habits include hexagonal prisms terminated by an hexagonal pyramid or a pinacoid, more commonly by both. Terminations can be rounded or dome-like but many have nice flat faces. Acicular, platy and fibrous forms are also seen.
  • Cleavage is poor and rarely seen.
  • Fracture is uneven.
  • Hardness is 2.5
  • Specific Gravity is approximately 1.8+ (well below average)
  • Streak is pale yellow.
  • Other Characteristics: Crystals are usually rather small, typically less than 1/4 inch long.
  • Notable Occurrences include the Kuruman District, South Africa.
  • Best Field Indicators are crystal habit, density, hardness, lack of cleavage, streak and color.



    

THE MINERAL SUGILITE

 


Sugilite is a somewhat obscure mineral named for the Japanese geologist who discovered the first specimens in 1944, Ken-ichi Sugi. It is becoming very popular in the jewelry trade. It does not form well shaped crystals but is usually massive. This is OK, as it is used mostly for ornamental and semiprecious stone purposes. It has a very distinctive opaque purple color when found in its most desirable color shades. The polished stones are mostly opaque with an almost waxy luster and a deep reddish purple color. It has been described as a purple turquoise although there is no relation between the two minerals. Its jewelry uses are becoming widespread and sugilite is being used in jewelry styles with turquoise, malachite and coral. Some sugilite has been cut into gemstones, but these are very rare.

The primary structural unit of sugilite is a most unusual double ring, with a formula of Si12O30. Normal rings of cyclosilicates are composed of six silicate tetrahedrons; Si6O18. The double ring is made of two normal rings that are linked together by sharing six oxygens, one from each tetrahedron in each six membered ring (notice the loss of six oxygens in the double ring formula). The structure is analogous to the dual wheels of a tractor trailer and is shared by other members of the Milarite - Osumilite Group.

 

PHYSICAL CHARACTERISTICS:

  • Color is purple, brown to yellow, pale pink and even black.
  • Luster is vitreous to dull or waxy.
  • Transparency: Crystals are translucent to opaque.
  • Crystal System is hexagonal; 6/m 2/m 2/m.
  • Crystal Habits include rare striated prismatic crystals, but specimens are usually massive.
  • Cleavage is poor in one direction.
  • Fracture is subconchoidal.
  • Hardness is 6 - 6.5
  • Specific Gravity is approximately 2.75 - 2.80 (average)
  • Streak is brown.
  • Associated Minerals include pectolite, poudretteite and polylithionite.
  • Notable Occurrences include the type locality of Iwagi Island, Shikoku, Japan as well as Mont Saint-Hilaire, Quebec, Canada and most importantly, South Africa.
  • Best Field Indicators are color, hardness, luster, streak and locality.

          

NATIVE SULFUR

 

 

  • Chemistry: S , Elemental Sulfur
  • CLASS: Elements
  • Uses: Major ore of sulfur which is used for chemical production
  • Specimens

Sulfur, which is given a bad reputation because of its odor, can make a very beautiful mineral specimen, and fine quality examples are much sought after. The unmistakable deep yellow color is not matched by any other mineral and the nicely shaped crystal forms of sulfur add to its attractiveness. As for the odor, this occurs when water mixes with the sulfur and a small amount of hydrogen sulfide (H2S) gas is produced. Although only small amounts of H2S form from just moisture in the air, it is a powerful odor producer and is the dominating contributor to the odor of rotten eggs. Rest assured, though, that most specimens of sulfur, when kept dry, do not emit a strong odor and this is not difficult for collectors of fine sulfur specimens to ensure.

 

PHYSICAL CHARACTERISTICS:

  • Color is a strong yellow color in thick crystals and duller yellow in small crystals to pale yellow in massive or powdery forms. Can also be reddish or greenish yellow with impurities.
  • Luster is vitreous to more often resinous or earthy in massive forms.
  • Transparency is transparent to translucent.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include mostly massive or powdery forms but well shaped blocky crystals are common. Crystals can be made up of two dipyramids, one with steeper faces than the other, prisms and/or pinacoids in various combinations.
  • Cleavage is very poor in two directions.
  • Fracture is conchoidal.
  • Streak is yellow.
  • Hardness is 2.
  • Specific Gravity is 2.0 - 2.1 (well below average)
  • Associated Minerals are celestite, calcite, aragonite and gypsum.
  • Other Characteristics: odor (see above), poor heat conductivity makes it brittle when heated and can actually crack if held tightly in a person's hand.
  • Notable Occurrences include Michigan and Ohio, USA; Sicily; Poland and Chile.
  • Best Field Indicators are color, odor, heat sensitivity, lack of good cleavage and crystal habit.

 

 

 

 

    

THE MINERAL SUOLUNITE

 

  • Chemistry: Ca2Si2O5(OH)2 - H2O, Hydrated Calcium Silicate Hydroxide.
  • Class: Silicates
  • Subclass: Sorosilicates
  • Group:Cuspidine - Wohlerite group
  • Uses: Only as mineral specimens.
  • Specimens

Suolunite is a very rare calcium silicate mineral. Its relatively simple chemistry defies the rarity of this mineral. The mineral forms deep within the Earth's crust near the mantle. Crystals can be colored a beautiful lavender to blue color and specimens are quite attractive.

 

PHYSICAL CHARACTERISTICS:

  • Color is lavender to sky blue, white or colorless.
  • Luster is vitreous to adamantine.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is triclinic; bar 1
  • Crystal Habits include bladed crystals and stellate aggregates and columnar specimens.
  • Cleavage is absent.
  • Hardness is 3.5
  • Specific Gravity is 2.7 (average).
  • Streak is white.
  • Associated Minerals are phlogopite, barite, apatite, priderite, hydroxyapophyllite, bultfonteinite, khibinskite, djerfisherite, titanite, monazite, witherite and perovskite.
  • Notable Occurrences are limited to the type locality from where it gets its name, Suolun, Inner Mongolia, China as well as Black Lake Mine, Coleraine Township, Quebec and Lac de Gras, Northwest Territories, Canada; Kulaski, Bosnia-Herzegovina and Al Khawd, near Masqat, Oman.
  • Best Field Indicators crystal habit, color, hardness, cleavage and localities.

 

 

 

 

 

THE MINERAL SUSANNITE

 

  • Chemistry: Pb4SO4(CO3)2(OH)2 , Lead Sulfate Carbonate Hydroxide.
  • Class: Carbonates
  • Uses: Only as mineral specimens.
  • Specimens

Susannite is a rare cousin of the mineral leadhillite. The two minerals are dimorphs. A dimorph is a mineral that shares the exact same chemistry with another mineral, but their structures are different (di in latin means two and morph in latin means shape). Typically the different structures make the symmetries different as well. In this case, susannite is a trigonal mineral while leadhillite is monoclinic in symmetry. Susannite is the higher temperature phase of the two and forms when warm fluids oxidize the lead ore deposits. However, leadhillite is the stable form at normal temperatures and pressures and many specimens of susannite may actually have converted to leadhillite.

Such crystals are called paramorphs (para means along or alongside; but in this case, paramorph means same chemistries, but with different structures). Paramorphs are a type of pseudomorph (pseudo means false). A pseudomorph is a crystal that has its internal structure either altered or completely replaced by a different mineral; but still retains its outward shape. Often a pseudomorph is one in which the original mineral is completely different from the pseudomorphing mineral such as when quartz replaces riebeckite for example. In the case of susannite, the internal structure of susannite converts to the more stable structure of leadhillite but retains susannite's rhombohedral form. And since the two minerals are dimorphs, the chemistry stays the same and hence they are paramorphs!

But the confusion does not stop there. There actually is another mineral that has the same chemistry and . . . you guessed it . . . a different structure. The mineral is called macphersonite and is orthorhombic in symmetry. This makes susannite, leadhillite and macphersonite a complete set of trimorphs (the tri means . . . ah, enough already).

 

PHYSICAL CHARACTERISTICS:

  • Color is colorless, white, greenish or yellowish.
  • Luster is adamantine to resinous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is trigonal.
  • Crystal Habits include platy rhombohedral crystals that may actually be paramorphed into leadhillite.
  • Cleavage is perfect in one direction (basal).
  • Hardness is 2.5 - 3
  • Specific Gravity is 6.5 (very heavy for a translucent mineral)
  • Streak is white.
  • Other Characteristics Some specimens are fluorescent.
  • Associated Minerals include leadhillite, galena, anglesite, linarite and cerussite.
  • Notable Occurrences include the type locality at Susanna Mine, Leadhills, Lanarkshire, Strathclyde, Scotland and the Mammoth-Anthony Mine, Tiger, Pinal County, Arizona.
  • Best Field Indicators: Crystal habit, color, luster, density and locality.

   

THE MINERAL SUSSEXITE

 

  • Chemistry: MnBO2(OH), Manganese Borate Hydroxide.
  • Class: Carbonates
  • Subclass: Borates
  • Uses: a very minor ore of manganese and as mineral specimens.
  • Specimens

Sussexite is a metamorphic borate mineral. It was first described from the famous mines of Franklin, New Jersey, USA. The mines are located in Sussex County, from where sussexite gets its name. The site of first discovery is called the type locality. Other borates that call this locality their type locality include cahnite and roweite. Other borates found at Franklin, but described somewhere else, include canavesite, fluoborite and mcallisterite.

Sussexite forms a series with the mineral szaibelyite, MgBO2(OH). A series occurs when two or more elements can substitute for each other without much distortion to the crystal structure. Szaibelyite is rich in magnesium while sussexite is enriched in manganese. Sussexite usually contains some magnesium as well as up to 3% zinc. Sussexite forms fibrous veins and masses.

 

PHYSICAL CHARACTERISTICS:

  • Color is white, pink, yellowish white or straw yellow.
  • Luster is silky, pearly to earthy.
  • Transparency: Specimens are translucent.
  • Crystal System is orthorhombic.
  • Crystal Habits include fibrous veins and masses.
  • Cleavage is perfect.
  • Fracture is uneven.
  • Hardness is 3 - 3.5.
  • Specific Gravity is approximately 3.1 - 3.3 (slightly above average)
  • Streak is white.
  • Other Characteristics Non-fluorescent, unlike so many other Franklin minerals.
  • Associated Minerals include franklinite, calcite, pyrochroite and hematite.
  • Notable Occurrence include the type locality of Franklin, Sussex County, New Jersey and Chicagon Mine, Iron County, Michigan, USA and Gonzen Mine, Switzerland.
  • Best Field Indicators are crystal habit, locality, luster, color, non-fluorescence and density.

 

 

 

 

 

THE MINERAL SVANBERGITE

 

  • Chemistry: SrAl3PO4SO4(OH)6, Strontium Aluminum Phosphate Sulfate Hydroxide.
  • Class: Sulfates; although sometimes classified as a Phosphate.
  • Group: Beudantite
  • Uses: Only as mineral specimens.
  • Specimens

Svanbergite is a rare strontium mineral. It forms pseudocubic rhombohedrons. The crystals can look nearly cubic, but the angles between the faces are not exactly 90 degrees as is required for a true cube. Faces tend to be curved and striated. It forms from the hydrothermal alteration of igneous rocks and in some low grade metamorphic schists.

Svanbergite is a difficult mineral to classify in that it has both a phosphate anion group and a sulfate anion group. The phosphate anion group would normally dictate that svanbergite be classified in the Phosphate Class of minerals. But svanbergite's sulfate anion is intricate and essential in its structure, while the phosphate anions can be substituted for to at least a limited degree. Some other classification schemes may place svanbergite in the Phosphate Class however.

 

PHYSICAL CHARACTERISTICS:

  • Color is yellow, rose, honey-orange, reddish-brown to colorless.
  • Luster is vitreous to adamantine.
  • Transparency: Specimens are mostly translucent to small crystals being transparent.
  • Crystal System is trigonal.
  • Crystal Habits include pseudocubic rhombohedrons and modified rhombohedrons. Faces tend to be curved and striated.
  • Cleavage is perfect in one direction (basal).
  • Hardness is 5.
  • Specific Gravity is approximately 3.2 (slightly above average for non-metallic minerals).
  • Streak is white.
  • Associated Minerals include pyrophyllite, kyanite, quartz, topaz, tourmaline, hematite, andalusite and woodhouseite.
  • Notable Occurrences are limited to Horrsjoberg, Varmland, Sweden; Pomba, Brazil; Quartzite, La Paz County, Arizona; Bluebird Hill, Imperial County and the Champion Andalusite Mine on the western slopes of the White Mountain Peak in Mono County, California, USA.
  • Best Field Indicators are crystal habit, striations, color, hardness and locality.




    

THE MINERAL SYLVANITE

 

  • Chemistry: AgAuTe4, Silver Gold Telluride.
  • Class: Sulfides
  • Subclass: Tellurides
  • Uses: A very minor ore of silver and gold and as mineral specimens.
  • Specimens

Sylvanite is one of the few minerals that is an ore of gold, besides native gold itself. It is one of the most common gold bearing minerals. 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 sylvanite 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 attraction to tellurium. Other gold tellurides include calaverite, (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 the more common sylvanite and differs in silver content and slightly in hardness, cleavage, color and density. At times the two minerals are only distinguishable with chemical tests.

Crystals of sylvanite are unique and of interest to collectors. Typically found as 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 a steel gray to silver gray to almost white.
  • 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 and columnar masses.
  • Cleavage is perfect in one direction.
  • Fracture is uneven.
  • Hardness is 1.5 - 2
  • Specific Gravity is approximately 8.2 (very heavy even for metallic minerals).
  • Streak is a steel gray to black.
  • Other Characteristics: Dark tarnish can often form after prolonged exposure to light.
  • Associated Minerals include gold, quartz, fluorite, rhodochrosite, pyrite, acanthite, nagyagite, calaverite, krennerite and other rare telluride minerals.
  • Notable Occurrences include Cripple Creek, Colorado and Calaveras County, California, USA; Nagyag, Romania; Bigstone Bay and Kirkland lake Gold District, Ontario and Rouyn District, Quebec, Canada; Kalgoorlie, Australia and Vahatala, Fiji.



       

THE MINERAL SYLVITE

 

  • Chemistry: KCl, Potassium Chloride
  • Class: Halides
  • Uses: As a major source of potash and as mineral specimens.
  • Specimens

Sylvite, also called sylvine, is a major source of potassium or potash used in fertilizer products. So great is the need for potassium that sylvite deposits are considered very valuable economically. As a mineral specimen sylvite does not get much attention. The crystals can be well formed and are often reddish due to inclusions of hematite. However, sylvite is very soluble in water and specimens need to be stored in closed containers because even the moisture in the air can degrade its appearance. Never clean a sylvite specimen with water!

Sylvite is closely related to the more common halite, NaCl, and they share so many properties that identification is sometimes difficult. Sylvite commonly has octahedral faces truncating the corners of the cubic crystals. So does halite, but this characteristic is much more prevalent in sylvite than in halite. Better tests include a taste test in which halite, salt, will taste salty and sylvite tastes bitter. This test is good if you need to distinguish one or two specimens, but what if you are testing hundreds of feet of core samples for beds of sylvite verses halite. A good test in those cases is the knife test in which a knife blade when scratched across the surface of the sample will produce a powder in halite and not in sylvite.

The name sylvite is easily confused with the much more valuable sylvanite. Sylvanite is a silver gold telluride, AuAgTe4 and should never be mistaken for sylvite.

 

PHYSICAL CHARACTERISTICS:

  • Color is colorless or white, sometimes tinted red, blue or yellow.
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is isometric; 4/m bar 3 2/m.
  • Crystal Habits are cubes with frequent octahedral faces truncating the corners of the cube, crystals will often have a cavernous appearance from dissolution. More commonly massive and granular.
  • Cleavage is good in three directions forming cubes.
  • Fracture is uneven.
  • Hardness is 2 - 2.5
  • Specific Gravity is 3.9 - 4.1 (heavier than average for translucent)
  • Streak is white.
  • Other Characteristics: Dissolves easily in water, does not powder when the blade of a knife is scratched across its surface and has a bitter taste, not salty like halite.
  • Associated Minerals include halite, carnallite, kieserite, gypsum, anhydrite and other evaporite minerals.
  • Notable Occurrences include Strassfurt, Germany; Kalush, Russia; New Mexico, Texas and Kern Co., California, USA; Saskatchewan, Canada; France, Mt. Vesuvius, Italy and Spain.
  • Best Field Indicators are bitter taste, associations and crystal habit.

 

 

 

THE MINERAL SYMPLESITE

 


Symplesite is a very rare iron arsenate mineral. It is dimorphous with the mineral parasymplesite. Both minerals have the same exact chemistry, but they have different structures resulting in different symmetries. Parasymplesite is monoclinic while symplesite is triclinic. The only notable difference between the two is symplesite's common blue color. Parasymplesite is isostructural with members of the Vivianite Group. While symplesite is not quite isostructural, it is closely related to minerals that would seem to make up their own meta group to the Vivianite Group. Such minerals as metakottigite and metavivianite are the triclinic dimorphs of the monoclinic minerals kottingite and vivianite. Maybe parasymplesite should be the triclinic dimorph instead of symplesite.

 

PHYSICAL CHARACTERISTICS:

  • Color is blue, deep blue, greenish blue or green.
  • Luster is vitreous to pearly.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is triclinic.
  • Crystal Habits include spherical aggregates and crusty powders.
  • Cleavage is perfect.
  • Fracture is uneven.
  • Hardness is 2.5
  • Specific Gravity is approximately 3.0 - 3.1 (average for translucent minerals).
  • Streak is white.
  • Associated Minerals are kottigite, pyrite, lollingite and parasymplesite
  • Notable Occurrences include Alsace, France; Custer County, South Dakota, USA; Lobenstein, Germany; Italy; Tasmania, Australia and Japan.
  • Best Field Indicators are color, crystal habit, cleavage, softness and associations.

 

 

 

THE MINERAL SYNCHYSITE

 

  • Chemistry: Ca(Ce, La, Nd, Y)(CO3)2F , Calcium Cerium Lanthanum Neodymium Yttrium Carbonate Fluoride.
  • Class: Carbonates
  • Groups: Rare earth carbonates and Bastnasite.
  • Uses: As a minor ore of cerium and other rare earth metals and as mineral specimens.
  • Specimens

Synchysite is one of a few rare earth carbonate minerals. Some of the other more common rare earth carbonates are ancylite, carbocernaite, tengerite, lanthanite, parisite, ewaldite, burbankite, donnayite and bastnasite.

Synchysite has cerium, neodymium, lanthanum and yttrium in its generalized formula but officially the mineral is divided into three minerals based on the respective predominant rare earth element. There is synchysite-(Ce) with a more accurate formula of Ca(Ce, La)(CO3)2F. There is also synchysite-(Nd) with a formula of Ca(Nd, La)(CO3)2F. And finally there is the very rare synchysite-(Y) with a formula of Ca(Y, Ce)(CO3)2F. There is little difference in the three in terms of physical properties and most synchysite is synchysite-(Ce).

Synchysite is closely related to three other distinct minerals; parisite, bastnasite and rontgenite-(Ce) The four are all rare earth fluoro-carbonates of similar formulas and occurrence. In Fact the four are often intergrown and a single crystal of any of these minerals probably contains at least one of the other minerals and possibly all four. As expected they can be difficult to distinguish from one another. One unique method involves the dissolvability of the four minerals in acids. Bastnasite is nearly indissolvable in cold nitric acid followed by parisite's slow dissolution, while rontgenite readily dissolves and synchysite dissolves the quickest. With a practiced hand, identification of samples can be made by gauging the rates of dissolution. Differing dissolution rates within a single crystal can also confirm the multiple phases or species that exist within the crystal, but this also tends to ruin the specimen. The zoning of different phases is not generally visible in untested specimens. Crystals often will show a zoning of inclusions but these do not indicate the boundaries of phases.

Synchysite was first discovered in the alkali- and hyperalkali-pegmatitic syenites of Narsarsuk, Greenland. Samples were originally described as parisite until the two minerals were conclusively separated in 1953 along with the establishment of bastnasite and rontgenite as distinct species as well. Synchysite's name is loosely derived from the Greek as "co-fluid" possibly alluding to these closely intermingled minerals.

As mineral specimens, synchysite has a wonderful crystal habit, nice luster and interesting color. Although usually the crystals are small and make excellent micromount specimens, they are generally well developed especially in specimens from Mont Saint-Hilaire. Their typical crystal habit is pseudohexagonal prisms that taper to a point or are bluntly terminated by a flat pinacoid face. The tendancy to thin and then widen repeatedly within the same crystal often yields a crystal shape that reminds one of an accordian. Weloganite is another carbonate mineral with a very similar crystal habit.

 

PHYSICAL CHARACTERISTICS:

  • Color is yellow, brown, yellow-orange, amber, pale green and white.
  • Luster is vitreous, greasy to dull.
  • Transparency: Crystals are translucent to opaque.
  • Crystal System is monoclinic (but pseudohexagonal).
  • Crystal Habits include small pseudohexagonal prismatic crystals that can taper in and out giving an accordion like look. Tabular or platy crystals are also seen as well as in rosettes, spheres and subhedral grains.
  • Cleavage is fair in one direction (basal).
  • Fracture is subconchoidal to splintery.
  • Hardness is 4 to 4.5.
  • Specific Gravity is 3.9 to 4.0 (above average)
  • Streak is white to yellowish white.
  • Other Characteristics: Easily soluble in nitric acid and crystals are striated parallel to the basal face.
  • Associated Minerals are extensive and include fluorite, galena, aegirine, albite, hematite, zircon, pyrochlore, astrophyllite, quartz, parisite, magnetite, anatase, smithsonite, rutile, siderite, cerussite, riebeckite, bastnasite, rontgenite-(Ce), ankerite, calcite, carbocernaite, cordylite, dolomite, strontianite, sahamalite-(Ce), apatite, chlorite, biotite, catapleiite, sphalerite, barite, monazite and xenotime.
  • Notable Occurrences include the type locality of Narsarsuk, Greenland. Other localities include the Clara Mine, Germany; Kola Peninsula, Russia; the mines of Mont Saint-Hilaire and at Gatineau, Quebec and the Thor Lake deposits, Northwest Territories, Canada; Cuasso al Monte, Italy; Adiounedj, Mali; langesundsfjord area, Norway; the Baerzhe deposit, Daxinganling Mountains, China; various karst bauxite sites in the Balkans especially at Grebnik Mountain, Serbia which is the type locality for synchysite-(Nd) and Scrub Oaks Mine, Dover, New Jersey, USA which is the type locality for synchysite-(Y).
  • Best Field Indicators: crystal habit, color, cleavage, density, luster, solubility in nitric acid and locality.
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