Wednesday, August 24, 2011

Mineral T


 

THE MINERAL TAAFFEITE

 


Taaffeite is a beautiful and rare gem mineral. It is one of those odd minerals that was first discovered from already cut and misidentified gemstone specimens. The gems were thought to be mauve spinels. But the discoverer and subsequent lender of his name, Count Taaffe realized that these "spinels" were doubly refractive. Something that is impossible with the isometric spinel. Taaffeite has properties that are very similar to spinel such as hardness, density and index of refraction and is therefore difficult to distinguish from the much more common gemstone spinel. Its the double refraction that is the key and the only way that most of the gem quality taaffeite has been found among the other gemmy grains found in alluvial deposits in Sri Lanka. Some lower grade taaffeite has been found in China associated with fluorite. But an original source for the taaffeite grains has yet to be discovered!

 

PHYSICAL CHARACTERISTICS:

  • Color is pink (mauve) or violet.
  • Luster is vitreous to adamantine.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is hexagonal; 6 2 2
  • Crystal Habits: Crystals are limited to alluvial grains.
  • Cleavage is absent.
  • Hardness is 8 - 8.5
  • Specific Gravity is 3.6+ (above average for translucent minerals)
  • Streak is white.
  • Associated Minerals include other alluvial gemstones such as spinel and also with fluorite.
  • Other Characteristics: Weakly pleochroic (different color shades can be seen from different viewing angles), index of refractive is around 1.72.
  • Notable Occurrences include the alluvial deposits in Sri Lanka and sediments in China
  • Best Field Indicators include double refraction, hardness, locality and color.

 

 

 

THE MINERAL TAINIOLITE

 


Tainiolite, which is named from the Greek for band or strip, is certainly not a well know mineral. An alternate and widely used spelling for tainiolite was taeniolite, but now tainiolite is the official spelling. Tainiolite is a rare mica mineral. It is a true mica closely related to other lithium rich micas; lepidolite and polylithionite. Tainiolite, like other micas, has a layered structure of lithium aluminum silicate sheets weakly bonded together by layers of potassium ions. These potassium ion layers produce the perfect cleavage. Tainiolite is easily confused with polylithionite but is comepletely non-fluorescent unlike polylithionite.

 

PHYSICAL CHARACTERISTICS:

  • Color is colorless, tan, brown to silvery.
  • Luster is vitreous to pearly.
  • Transparency crystals are transparent to translucent.
  • Crystal System is monoclinic; 2/m
  • Crystal Habits include thin lamellar tabular to platy crystals forming "books", scales and tapering prisms.
  • Cleavage is perfect in one direction producing thin sheets or flakes.
  • Fracture is not readily observed due to cleavage but is uneven.
  • Hardness is 2.5 - 3.
  • Specific Gravity is approximately 2.8 - 2.9 (average)
  • Streak is white.
  • Other Characteristics: Non-fluorecent as opposed to polythionite.
  • Associated Minerals are natrolite, fluorite, microcline, pectolite, quartz,phillipsite, richterite and aegirine, among other rare minerals.
  • Noteable Occurrences include the type locality of Narsarsuk, Greenland as well as Lovozero Massif, Kola Peninsula, Russia; Magnet Cove, Arkansas and Coyote Peak, Humboldt County, California, USA and Mont Saint-Hilaire, Quebec, Canada.
  • Best Field Indicators are crystal habit, non-fluorescence, color, cleavage, locality and associations.

 

 

 

 

   

THE MINERAL TALC

 

  • Chemistry: Mg3Si4O10(OH)2, Magnesium Silicate Hydroxide
  • Class: Silicates
  • Subclass: phyllosilicates
  • Group: Clays and also The Montmorillonite/Smectite Group.
  • Uses: an ornamental and heat, acid and electrically-resistant stone (soapstone) used as counter tops, electrical switchboards, carvings, etc, used as an ingredient in paints, rubber, roofing materials, ceramics and insecticides. Most commonly known as the primary ingredient in talcum powder.
  • Specimens

Talc is an important industrial mineral. Its resistance to heat, electricity and acids make it an ideal surface for lab counter tops and electrical switchboards. It is also an important filler material for paints, rubber and insecticides. Even with all these uses, most people only know talc as the primary ingredient in talcum powder. Mineral specimens are not very common as it does not form very large crystals. However, it often replaces other minerals on an atom by atom basis and forms what are called pseudomorphs (false shape). The talc takes the form of the mineral it replaces. A specimen of what looks like milky quartz is quite a suprise when it not only has a soapy feel but can be scratched by a fingernail.

 

PHYSICAL CHARACTERISTICS:

  • Color is green, gray and white to almost silver.
  • Luster is dull to pearly or greasy.
  • Transparency crystals are translucent and masses are opaque.
  • Crystal System is monoclinic; 2/m.
  • Crystal Habits: never in large individual crystals, but if found are flattened tabular crystals with a hexagonal cross-section, usually talc is found in compact or lamellar masses. Forms pseudomorphs (false shape) of other crystals such as quartz, pyroxenes, olivine and amphiboles.
  • Cleavage is perfect in one direction, basal.
  • Fracture is uneven to lamellar.
  • Hardness is 1 (can leave mark on paper)
  • Specific Gravity is 2.7 - 2.8 (average)
  • Streak is white.
  • Other Characteristics: cleavage flakes are slightly flexible but not elastic and talc has a soapy feel to the touch.
  • Associated Minerals include serpentine, dolomite, magnesite, quartz, pyroxenes, olivine, biotite and amphiboles.
  • Notable Occurances: include many mines up and down the Appalachian Mountains and in California and Texas, USA; Germany; Florence, Italy; Tyrol, Austria; Transvaal, South Africa and Shetland, Scotland.
  • Best Field Indicators softness, color, soapy feel, luster and cleavage.



   

THE MINERAL TANTALITE

 

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

Tantalite is the most widespread tantalum mineral and makes for an important ore of the industrially useful metal. Tantalum is used in alloys for strength and higher melting points, in glass to increase the index of refraction, and in surgical steel, as it is non-reactive and non-irritating to body tissues.

Tantalite forms a series with the mineral columbite. In fact the two are often grouped together as a semi-singular mineral called columbite-tantalite in many mineral guides. A series is where two or more elements can occupy the same places within a crystal structure and their respective percentages can then vary. The two minerals of this series have similar properties since they have the same structure and similar chemistries (tantalum and niobium are very similar elements). Tantalite is the more tantalum rich end member and columbite is the more niobium rich end member. Niobium had been called columbium hence the name columbite.

Tantalite's greatest difference from columbite is its much greater specific gravity, 8.0+ compared to columbite's 5.2. Other properties that vary slightly are color, transparency and streak. Both minerals can be found more or less together in granitic pegmatites rich in lithium and phosphorus minerals with columbite concentrated at the edges of the pegmatite and tantalite enriched in the core.

Tantalite has a series of its own. The iron and manganese amounts vary considerably without much effect on properties. However the two end members are recognized as distinct minerals although collectors have found this to be rather cumbersome and generally prefer tantalite to the non-unique names of ferrotantalite and manganotantalite.
Tantalite has a dimorphic relationship to another mineral called tapiolite. A dimorph is a mineral that has the same chemistry but a different structure. Tapiolite has a tetragonal structure as opposed to the orthorhombic structure of tantalite although it has exactly the same chemistry, (Fe, Mn)(Ta, Nb)2O6.
As mineral specimens, tantalite can be a nice addition to one's collection. Good crystals are both complex and handsome. Although the color selection is usually limited too black to brown the luster is generally good. Manganese rich tantalites can be brown and translucent.

 

PHYSICAL CHARACTERISTICS:

  • Color is dark black, iron-black to dark brown or even reddish brown.
  • Luster is submetallic to almost resinous.
  • Transparency: Crystals are nearly opaque being transparent in thin splinters.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include stubby prismatic crystals with complexly faceted or rounded terminations. Also very flat tabular crystals sometimes aggregated together in parallel or nearly parallel groups. Can also be granular and massive.
  • Cleavage is good in one direction.
  • Fracture is subconchoidal.
  • Hardness is 6 - 6.5
  • Specific Gravity is approximately 8.0+ when pure (very heavy for non-metallic minerals).
  • Streak is brownish-red to black.
  • Other Characteristics: Some specimens may show a bluish iridescent tarnish and demonstrate weak magnetism.
  • Associated Minerals include albite, spodumene, cassiterite, microcline, lepidolite, apatite, beryl, microlite, tourmalines and amblygonite.
  • Notable Occurrences include Newry, Maine; San Diego Co., California; Colorado and Amelia, Virginia, USA; Renfrow County, Ontario, Canada; Madagascar; Sweden; Norway and Finland.
  • Best Field Indicators are crystal habit, streak, associations and specific gravity.



 

 

TANZANITE,

THE GEMSTONE VARIETY OF ZOISITE

 

VARIETY INFORMATION:

  • VARIETY OF: Zoisite, Ca2Al3(SiO4)3(OH), Calcium Aluminum Silicate Hydroxide.
  • USES: Gemstone
  • COLOR: various shades of blue to lavender, deeper along the crystal axis.
  • INDEX OF REFRACTION: 1.68 - 1.72
  • BIREFRINGENCE: is good
  • HARDNESS: 6.5-7
  • CLEAVAGE: perfect in one direction
  • CRYSTAL SYSTEM: orthorhombic

Tanzanite is relatively new on the gemstone market, but has left its mark. Its blue-lavender color is rather unique and a wonderful addition to the gemstone palette. Found in Tanzania (hence the name) in 1967, it has since become a well known and widely distributed gemstone. It has become so popular that in October of 2002 the American Gem Trade Association (AGTA) announced that tanzanite had joined zircon and turquoise in the traditional list of birthstones for the month of December.

It has better fire than the tourmaline elbaite or peridot and an adequate hardness. Its only one direction of cleavage is somewhat of a problem because it is oriented with the direction of strongest pleochroism. This would be a problem in most gemstones because that is the direction the gemcutter would usually select to maximize the color. However, with tanzanite the color is usually strong enough anyway.

Pleochroism is very pronounced in tanzanite and is seen as three different color shades in the same stone. In the viewing a tanzanite stone, the colors dark blue, green-yellow and red-purple can be seen, all a result of pleochroism. Lesser stones may have a brownish color due to the mixing of blue, purple and green. These stones are usually heat treated to a deep blue color. Iolite is a blue-violet gemstone variety of the mineral cordierite, has strong pleochroism and can be confused with tanzanite. However, iolite is usually less strongly colored, its pleochroic colors vary from blue-violet to yellowish gray to blue and it has less fire. Iolite's unusual color shades makes it an exotic colored gemstone whose popularity is growing day by day.
Nearly all tanzanite has been heat treated to generate the beautiful violet-blue color this stone is known for.  When first mined, most stones are a muted green color. The only known source of Tanzanite is a five square mile hilltop at Merelani, ten miles south of the Kilimanjaro International Airport in Tanzania.


 

 

THE MINERAL TARBUTTITE

 

  • Chemistry: Zn2(PO4)(OH), Zinc Phosphate Hydroxide.
  • Class: Phosphates
  • Uses: only as a mineral specimen.
  • Specimens

Tarbuttite is a somewhat rare phosphate mineral but is popular among collectors of rare minerals, especially rare phosphates. It forms good crystals and has a nice luster. Occasionally, the colors can be rather attractive although they are commonly known to be pale. It is usually associated with the colorful limonite, an iron oxide, and the combination can make for a nice cabinet specimen.

 

PHYSICAL CHARACTERISTICS:

  • Color is colorless and pale white, red, green, yellow or brown.
  • Luster is vitreous.
  • Transparency crystals are transparent to translucent.
  • Crystal System is triclinic, bar 1
  • Crystal Habits include deeply striated prismatic crystals or crusts.
  • Cleavage is perfect in one direction.
  • Hardness is 3.5 - 3.7
  • Specific Gravity is approximately 4.2 (heavy for translucent minerals)
  • Streak is white.
  • Associated Minerals are limonite, smithsonite and some other oxidized zinc ore deposit minerals.
  • Notable Occurrences include Broken Hill, Shaba, Zambia and elsewhere.
  • Best Field Indicators are crystal habit, locality, associations with other zinc ores and/or phosphate minerals and density.



TEKTITES

Tektites are still poorly understood. They are irregularly- and at times intricately-shaped nodules and blobs of a glassy substance. They have no crystal structure, and are therefore similar to obsidian, but are not associated with volcanic processes. Their chemistry is unique and somewhat unexplained.

The leading theory concerning their origin is the "Meteorite Impact Theory". It is postulated that many odd events occur during a meteor's impact because of the tremendous heat and pressure produced. Tektites may be fused glass that formed during an impact of a meteor with layers of rock on the Earth's surface. Tektites occur in broad bands in specific localities in different parts of the world. These bands produce characteristically similar tektites and are sometimes loosely associated with meteorite craters or suspected craters. Could these fields represent splash material from an impact? Many believe so and this idea is gaining acceptance from many scientists. The odd and diverse chemistry of the tektites could be a result of unique meteorites hitting unique rock types with the combinations producing particular effects.

Some tektites, called Moldavites, are especially prized for their clarity and unique green color. Moldavites are found in a "splash field" centered around Moldavia in former Czechoslovakia and are believed to have come from a meteorite crater in Germany. Moldavites are sometimes cut as gemstones or put into jewelry as natural uncut pieces to show off their often eerie and beautifully intricate shapes.

 

PHYSICAL CHARACTERISTICS:

  • Color is black, green or colorless.
  • Luster is vitreous to dull.
  • Transparency: Gemmy tektites are transparent to translucent, but most are nearly opaque.
  • Crystal System does not apply because tektites are amorphous.
  • Habits are usually small nodules or splinters that vary from simple rounded shapes to very intricate natural carvings. Many have smooth, scarred, or pitted surfaces.
  • cleavage is absent.
  • Fracture is conchoidal.
  • Hardness is 5 - 6.
  • Specific Gravity is approximately 2.5 (somewhat light).
  • Streak is white.
  • Other Characteristics: Can sometimes be directly associated with meteorite impact craters.
  • Notable Occurrences include Moldavia region of Eastern Europe; Thailand and southeast Asia; Australia and Georgia, USA.
  • Best Field Indicators are color, odd shapes, localities and lack of cleavage or crystal faces.



     

THE MINERAL TELLURIUM

 

  • Chemistry: Te, Elemental Tellurium
  • Class: Elements
  • Uses: A minor ore of tellurium and as mineral specimens.
  • Specimens

Native tellurium is a rare mineral. When it does occur it is often found with gold and gold tellurides such as sylvanite and calaverite.

The metal tellurium is mostly used in alloys with other metals. It is added to lead to improve its strength and durability. In steel and copper it makes the metals more workable. Tellurium is also used in blasting caps.

 

PHYSICAL CHARACTERISTICS:

  • Color is tin white often with a muted multi-colored iridescent tarnish.
  • Luster is metallic.
  • Transparency: Crystals are opaque.
  • Crystal System is trigonal; 3 2
  • Crystal Habits include prismatic crystals but more commonly massive as vein fillings.
  • Cleavage is good in three directions (prismatically) and poor in a fourth (basal).
  • Fracture is uneven.
  • Hardness is 2 - 2.5
  • Specific Gravity is 6.1 - 6.3 (unusually heavy even for metallic minerals)
  • Streak is tin white.
  • Associated Minerals include poughite, gold, sylvanite and calaverite.
  • Notable Occurrences include Lincoln County, Nevada, New Mexico and at Cripple Creek, Colorado, USA; Romania and Australia.
  • Best Field Indicators are tarnish, density, color and cleavage.

 

 

 

 

 

THE MINERAL TENNANTITE

 

  • Chemistry: Cu12As4S13, Copper Arsenic Sulfide
  • Class: Sulfides
  • Group: Tetrahedrite
  • Uses: ore of copper and a minor ore of silver and arsenic.
  • Specimens

Tennantite forms a series with the much more common mineral tetrahedrite (Cu12Sb4S13, Copper Antimony Sulfide). The two share the same crystal structure but they differ in the percentage of arsenic versus antimony. Antimony rich specimens are tetrahedrite while arsenic rich specimens are tennantite. Some iron, zinc and/or silver always substitute for the copper in both minerals up to approximately 15 % .

It is difficult to distinguish the two minerals by ordinary means. Tennantite is generally darker, has a redder streak and a translucent red color that can be seen in thin splinters when they are held up to a strong light. Tetrahedrite is by far the more common of the two. Tetrahedrite is named for the common form, the tetrahedron, that both tennatite and tetrahedrite form.

The tetrahedron is an interesting isometric crystal form. It is obvious where the four three fold axes of the isometric system belong, as each one exits out of the crystal through each of the four identical "pyramidal" peaks. However the four fold axes are evidently missing. They aren't, they are just four fold rotoinversion axes. A four fold rotoinversion axis takes a face, rotates it 90 degrees (one fourth of a rotation) and then inverts it (up to down & right to left) through the crystal to the other side. Then it rotates it again 90 degrees and inverts it again through the crystal. Another rotoinversion operation and finally another (four in all) and the face is back, exactly where it started. The result is two faces on the "top" and two on the "bottom" of the crystal but in perpendicular orientation. The tetrahedral faces of tennantite are in many instances modified by other crystal forms giving the crystals multiple facets while still retaining the overall tetrahedral shape.

Tennantite is in an informal group of minerals called the "fahlerz" or "fahlores" group. The group is named for an old german miners word meaning "pale ore". Most members of the tetrahedrite group belong to this informal group.
Although rarer than its cousin, tennantite forms nice crystals and can be a handsome specimen. Often tennantite will contain a certain percentage of silver and be used as a minor ore. Collectors usually crave nice specimens of verified tennantite.

 

PHYSICAL CHARACTERISTICS:

  • Color is black to steel gray.
  • Luster is metallic.
  • Transparency crystals are opaque.
  • Crystal System is isometric; bar 4 3m
  • Crystal Habits of course include the tetrahedron sometimes modified by the dodecahedron and tristetrahedron. Twinning is occassionally seen. Also massive and granular.
  • Cleavage is absent.
  • Fracture is subconchoidal.
  • Hardness is 3 - 4.
  • Specific Gravity is approximately 4.6 (average for metallic minerals)
  • Streak is black to reddish if rubbed.
  • Associated Minerals are quartz, pyrite, arsenopyrite, chalcopyrite and other sulfides.
  • Other Characteristics: thin splinters can have a translucent red color.
  • Notable Occurances include Bennatal, Switzerland; Tsumeb, Namibia; Saxony, Germany and Butte, Montana, USA.
  • Best Field Indicators are crystal habit, lack of cleavage, streak and color.

THE MINERAL TEPHROITE

 


Tephroite is one of the unusual minerals found at the famous mines of Sterling Hill and Franklin, New Jersey, USA. It is named for the typical color which is ash gray ("tephros" is Greek for ash colored). Tephroite forms a series with the olivine mineral fayalite. Tephroite is the manganese rich member of the series and fayalite is the iron rich member with a formula of Fe2SiO4. Unlike fayalite which is more commonly found in volcanic rocks, tephroite is a contact metamorphic and hydrothermal replacement mineral.

 

PHYSICAL CHARACTERISTICS:

  • Color is commonly ash gray but also is found olive-green, greenish-blue, pink or brown.
  • Luster is vitreous to greasy.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include short prismatic to blocky crystals Also massive, granular and compact.
  • Cleavage is good in two directions at 90 degrees.
  • Fracture is uneven to conchoidal.
  • Hardness is 6
  • Specific Gravity is approximately 4.1 (heavy for non-metallic minerals)
  • Streak is off white to gray.
  • Associated Minerals are calcite, quartz, spessartine, rhodonite, willemite, franklinite and pyroxmangite.
  • Notable Occurrences include the Sterling Hill and Franklin, New Jersey and California, USA locations; Cornwall, England and Langban, Sweden.
  • Best Field Indicators are crystal habit, cleavage, environment, color, hardness and density.



 

  

THE MINERAL TETRAHEDRITE

 


Tetrahedrite forms a solid solution series with the rather rare mineral tennantite (Cu12As4S13, Copper Arsenic Sulfide). The two share the same crystal structure but they differ in the percentage of arsenic versus antimony. Antimony rich specimens are tetrahedrite while arsenic rich specimens are tennantite. Some iron, zinc and/or silver always substitute for the copper in both minerals up to approximately 15 % .

Tetrahedrite is named for its common crystal form, the tetrahedron. The tetrahedron is an interesting isometric crystal form. It is obvious where the four three fold axes of the isometric system belong, as each one exits out of the crystal through each of the four identical "pyramidal" peaks. However the four fold axes are evidently missing. They aren't, they are just four fold rotoinversion axes. A four fold rotoinversion axis takes a face, rotates it 90 degrees (one fourth of a rotation) and then inverts it (up to down & right to left) through the crystal to the other side. Then it rotates it again 90 degrees and inverts it again through the crystal. Another rotoinversion operation and finally another (four in all) and the face is back, exactly where it started. The result is two faces on the "top" and two on the "bottom" of the crystal but in perpendicular orientation. The tetrahedral faces are in many instances modified by other crystal forms giving the crystals multiple facets while still retaining the basic tetrahedral shape.

Tetrahedrite is in an informal group of minerals called the "fahlerz" or "fahlores" group. The group is named for an old german miners word meaning "pale ore". Most members of the tetrahedrite group belong to this informal group.

Tetrahedrite can form interesting and handsome mineral specimens. Often it will contain a certain percentage of silver and be used as a minor ore. The multi-faceted tetrahedral crystals as well as the flat faced simple tetrahedral crystals can be very striking and a real pleasure for mineral collectors to own.

 

PHYSICAL CHARACTERISTICS:

  • Color is black to steel gray to silver.
  • Luster is metallic.
  • Transparency crystals are opaque.
  • Crystal System is isometric; bar 4 3m
  • Crystal Habits of course include the tetrahedron sometimes modified by the dodecahedron and tristetrahedron. Twinning is occassionally seen. Also massive and granular.
  • Cleavage is absent.
  • Fracture is conchoidal.
  • Hardness is 3 - 4+.
  • Specific Gravity is approximately 4.6 - 5.1 (average for metallic minerals)
  • Streak is black to brown.
  • Associated Minerals are quartz, pyrite, galena, chalcopyrite and other sulfides.
  • Other Characteristics: tarnishes to a greenish shade.
  • Notable Occurances include Peru; Broken Hill, Australia; Mexico; Germany and others.
  • Best Field Indicators are crystal habit, lack of cleavage and color.



 

 

THE MINERAL THAUMASITE

 

  • Chemistry: Ca3Si(CO3)(SO4)(OH)6 - 12H2O, Hydrated Calcium Silicon Carbonate Sulfate Hydroxide.
  • Class: Sulfates
  • Group: Ettringite
  • Uses: Only as mineral specimens.
  • Specimens

Thaumasite is a fairly rare mineral. Its chemistry and classification are interesting. It is sometimes classified as a silicate due to its silicon content and there is an argument to be made for its classification as a carbonate as well. However it does belong to a predominantly sulfate mineral group, the Ettringite Group and its properties seem more in line with its inclusion into the sulfate class.

Four out of every five atoms in this mineral is either a part of a water molecule or an hydroxide. It's almost all water! This fact is reflected in its very low specific gravity of only 1.9, that's less than twice the specific gravity of water.

 

PHYSICAL CHARACTERISTICS:

  • Color is colorless or white.
  • Luster is vitreous.
  • Transparency: Crystals are translucent.
  • Crystal System is trigonal; bar 3 2/m.
  • Crystal Habits include acicular crystals and massive forms.
  • Cleavage is poor and rarely seen.
  • Fracture is uneven.
  • Hardness is 3.5
  • Specific Gravity is approximately 1.9 (well below average)
  • Streak is white.
  • Associated Mineral is commonly spurrite.
  • Notable Occurrences include Crestmore, Riverside Co., California and Paterson, New Jersey, USA and Langban, Sweden.
  • Best Field Indicators are density, hardness and association.

   

THE MINERAL THENARDITE

 

  • Chemistry: Na2SO4, Sodium Sulfate.
  • Class: Sulfates
  • Uses: As a source of sodium to produce soda, various uses in the glass and paper industries and as mineral specimens.
  • Specimens

Thenardite is one of several non-marine evaporite Sulfate Class minerals. It is easily dissolvable in water and specimens should be stored with desiccant. Sulfates in general tend to be more soluble than most of the other mineral classes and simple sodium salts, such as thernardite, are always soluble. As one might imagine, thenardite forms in arid regions as a salty precipitate as well as in dry caves and mines as an efflorescence and as a crusty deposit around fumaroles. It is associated with other minerals that form in the deposits of playa lakes.

Thenardite, which is named for the French chemist Louis J. Thenard, has several distinctive properties in addition to its solubility. For one it has a salty taste similar to halite, but the different cleavages and crystal habits make the two minerals quite distinguishable from each other. Thenardite is also generally fluorescent showing a white color in shortwave UV and a yellow-green color in longwave UV. Thenardite also has a distinctive crystal habit in which crystals form a diamond-like shape (such as from a deck of cards). The crystals are generally flattened and are sometimes well formed showing good orthorhombic symmetry. Although not often seen in mineral shops, thenardite is now making a presence with well formed crystal clusters mostly coming from Searles Lake, San Bernardino County, California.

Thenardite specimens should be stored in closed containers as thenardite is only metastable. The specimens will gradually absorb water and convert to the mineral mirabilite. In volcanic caves on Mt. Etna, Italy; thenardite is an early secondary mineral forming the cave's speleothems. But when the temperature of the cave lowers and the humidity rises, the thenardite coverts to mirabilite.

 

PHYSICAL CHARACTERISTICS:

  • Color is typically gray, white, colorless or brownish white or yellowish white.
  • Luster is vitreous, pearly to resinous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is orthorhombic: 2/m 2/m 2/m.
  • Crystal Habits include tabular, dipyramidal, flattened, diamond-shaped crystals; often intergrown. Twins form arrowhead like crystals and crossed interpenetration twins. Also as crusts, granular and as massive rock forming beds.
  • Cleavage is perfect in one direction (pinacoidal).
  • Fracture is uneven to hackly or splintery.
  • Hardness is 2.5 - 3.
  • Specific Gravity is approximately 2.7 (average for translucent minerals).
  • Streak is white.
  • Other Characteristics: Easily soluble in water, has a salty taste, is fluorescent white in shortwave UV and yellow-green in longwave UV and can color a flame yellow (for sodium).
  • Associated Minerals include halite, mirabilite, gypsum, glauberite, trona, blodite, alunite, picromerite, sborgite, borax and other borate and non-marine evaporite minerals.
  • Notable Occurrences include several California sites such as Searles Lake, San Bernardino County; Soda Lake, San Luis Obispo County; Bertram deposit, Imperial County and Furnace Creek district, Inyo County; as well as Camp Verde Yavapi County in Arizona and sites in Nevada, USA; Espartinas, Madrid Province, Spain; Siberia, Russia; Mt Etna, Sicily, Italy; Chile; Kazakhstan and Canada.
  • Best Field Indicators are crystal habit, environment of formation, associations, cleavage, taste and fluorescence.

 

 

 

 

 

 

THE MINERAL THOMSONITE

 


Thomsonite is one of the rarer zeolites. It forms tight acicular radiating clusters and sphericules as well as some blockier crystals that are found in the vesicles or bubbles of volcanic rock as are most other zeolites. Natrolite, another zeolite, is usually square in cross section but is otherwise difficult to distinguish from thomsonite. The color is usually colorless or white, but a few specimens have shown a lovely yellow color. Thomsonite is a rare mineral and is sought after by collectors of rare zeolite minerals.

Zeolites are known to have an openness about their structure that allows large ions and molecules to reside and actually move around inside the overall framework. The structure actually 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 can act as a chemical sieve, allowing some ions to pass through while blocking others.

 

PHYSICAL CHARACTERISTICS:

  • Color is clear, white and yellow .
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is orthorhombic.
  • Crystal Habits include tight acicular radiating clusters and sphericules. Blocky, prismatic, fibrous and tabular crystals are also known.
  • Cleavage is perfect.
  • Fracture is uneven.
  • Hardness is 5 - 5.5
  • Specific Gravity is approximately 2.2 - 2.4 (light).
  • Streak is white.
  • Associated Minerals are quartz, calcite, chabazite, natrolite, heulandite, stilbite and other zeolites.
  • Notable Occurrences include Saxony, Germany; Italy; Faroe Islands; Kilpatrick Hills, Scotland and Kern Co., California and Cape Lookout, Oregon, USA.
  • Best Field Indicators are crystal habit, density, hardness and associations.



 

    

THE MINERAL THORITE

 

  • Chemistry: (Th, U)SiO4, Thorium Uranium Silicate.
  • Class: Silicates
  • Subclass: Nesosilicates
  • Uses: As a minor ore of thorium and uranium and as mineral specimens.
  • Specimens

Thorite is the most common thorium mineral. Thorium is a highly radioactive element and could be used as a replacement for uranium in nuclear power generation. It is estimated to be three times as common as uranium and all the thorium in the Earth's crust could have more potential energy than both uranium and the fossil fuel reserves combined. Uranium and thorium are considered to be the primary sources of the internal heat of the Earth through their radioactive decay.

Although thorite is the most common thorium mineral, it is not the primary ore of thorium. The phosphate mineral monazite has an average of about 6% thorium in its composition that includes several rare earth elements. Enough monazite is mined to supply most of the current thorite demand. If monazite deposits become scarce or the demand for thorium increases, then thorite and to lesser extents other thorium bearing minerals such as thorianite, thorogummite , huttonite and thorutite will gain greatly in importance.

Thorite is currently an important ore of uranium. A variety of thorite often called "uranothorite" is particularly rich in uranium and has been a viable uranium ore at Bancroft, Ontario, Canada. Other varieties of thorite include "orangite", an orange variety; "calciothorite" an impure variety with trace amounts of calcium and "freyalite" actually a discredited variety containing cerium (it turned out to be an altered form of the mineral melanocerite).
There is a closely related mineral to thorite called thorogummite that was once considered a variety of thorite but is a product of alteration to thorite. Thorogummite has some of the SiO4 tetrahedrons replaced by four hydroxides for a formula that looks like:
(Th, U)2(SiO4)(2 - X)(OH)4X

The X represents the conversion of one silicate tetrahedron with a negative four charge (-4) to four hydroxides with a negative one charge (-1) each. So that if half the silicate tetrahedrons are replaced by the four hydroxides, where X = 1, the formula would look like this:
(Th, U)2SiO4(OH)4

Thorite also is related to a mineral called huttonite. Thorite and huttonite are dimorphs. The two minerals have the same chemistry, they just have different structures, di means two and morph means shape. A similar situation occurs with the dimorphism of diamond and graphite, both of whom are composed of carbon, but have very different structures. Huttonite ironically belongs in the Monazite Group and is related structurally to its members.
Because thorite is highly radioactive, specimens are often metamict. This is a condition found in radioactive minerals and results from the destructive effects of its own radiation on its crystal lattice. The effect can destroy a crystal lattice completely while leaving the outward appearance unchanged. Thorogummite is believed to be formed from thorite by hydration which is facilitated by metamictation.

Specimens of thorite generally come from igneous pegmatites and volcanic extrusive rocks, hydrothermal veins and contact metamorphic rocks as well as small grains found in detrital sands. Crystals are rare, but when found can produce nicely shaped short prismatic crystals with pyramidal terminations. 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 normally black, but also brownish black, orange, yellowish-orange and dark green.
  • Luster is resinous.
  • Transparency: Crystals are opaque.
  • Crystal System is tetragonal; 4/m 2/m 2/m
  • Crystal Habits include short prismatic crystals with a square cross-section and simple pyramidal terminations. Also massive, embedded irregular grains and reniform.
  • Cleavage is poor, in two directions lengthwise, but is rarely seen.
  • Fracture is conchoidal.
  • Hardness is 4.5 - 5
  • Specific Gravity is 4.1 - near 7.
  • Streak is orange to brown.
  • Other Characteristics: Nearly always metamict and always strongly radioactive.
  • Associated Minerals include quartz, feldspars, biotite and betafite.
  • Notable Occurrences are found at Langesundfjord, Norway; Bancroft, Ontario, Canada; Eifel District, Germany and Arizona, USA.
  • Best Field Indicators are color, luster, crystal habit, fracture and especially radioactivity.



THE MINERAL THOROGUMMITE

  • Chemistry: (Th, U)2(SiO4)(2 - X)(OH)4X, Thorium Uranium Silicate Hydroxide.
  • Class: Silicates
  • Subclass: Nesosilicates
  • Uses: As a very minor ore of thorium and uranium and as mineral specimens.
  • Specimens

Thorogummite, once considered a variety of thorite, is actually a product of the alteration of thorite, (Th, U)SiO4. This alteration of thorite is caused by hydration facilitated by metamictation. Because thorite is highly radioactive, specimens are often metamict. This is a condition found in radioactive minerals and results from the destructive effects of its own radiation on its crystal lattice. The effect can destroy a crystal lattice completely while leaving the outward appearance unchanged. During this process, hydration of the structure can occur, forming a new mineral; thorogummite!

Thorogummite has varying amounts of SiO4 tetrahedrons that are replaced by four hydroxides. This can be represented with several different formulas. The formula that is used here:
(Th, U)2(SiO4)(2 - X)(OH)4X

The X represents the conversion of one silicate tetrahedron with a negative four charge (-4) to four hydroxides with a negative one charge (-1) each. So that if half the silicate tetrahedrons are replaced by the four hydroxides, where X = 1, the formula would look like this:
(Th, U)2SiO4(OH)4

Often though thorogummite's formula is written like this:
(Th, U)[SiO4, (OH)4]

This formula also reflects the substitution of hydroxides for silicate tetrahedrons.
Thorogummite is a very minor ore of thorium due to its association with thorite. However, the primary thorium ore is not thorite but the phosphate mineral monazite. It has an average of about 6% thorium in its composition that includes several rare earth elements. Enough monazite is mined to supply most of the current thorite demand. Other thorium bearing minerals includes, but is not limited to, thorianite, thorite, huttonite and thorutite.

Specimens of thorite, and therefore thorogummite, generally come from igneous pegmatites and volcanic extrusive rocks, hydrothermal veins and contact metamorphic rocks. Because this is an alteration product, thorogummite does not form well shaped crystals unless the outward morphology of the thorite crystal is left intact. In these cases the specimen is in reality a pseudomorph (pseudo = false, morph = shape) of thorite. 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 pale yellow or white.
  • Luster is earthy.
  • Transparency: Specimens are opaque.
  • Crystal System is tetragonal; 4/m 2/m 2/m
  • Crystal Habits include earthy masses and pseudomorphs of thorite which are short prismatic crystals with a square cross-section and simple pyramidal terminations.
  • Cleavage is absent.
  • Fracture is earthy.
  • Hardness is 1
  • Specific Gravity is 4.1 - 4.5.
  • Streak is pale yellow to white.
  • Other Characteristics: Always metamict and strongly radioactive.
  • Associated Minerals include quartz, feldspars, thorite, biotite and betafite.
  • Notable Occurrences are found at Langesundfjord, Norway and other thorite localities.
  • Best Field Indicators are color, luster, association with thorite and radioactivity.




THE MINERAL TIN

 


Native tin (the latin word for tin is stannum and gives tin its chemical symbol Sn) is a rare mineral. It is so rare that it in no way can it be thought of as an ore of tin. Tin ore minerals include the oxide minerals cassiterite and rutile and a few sufides such as franckeite, cylindrite, canfieldite, stannite and teallite. By far the most tin comes from cassiterite; SnO2. The largest tin producers are China and Indonesia followed by Peru, Brazil, Bolivia and Australia. The United States which has significant resources for most industrial metals is found quite lacking in tin. Alaska has the only viable source of tin in the United States and it is insignificant compared to other world sources.

Pure tin metal has few uses and thus most tin is used in alloys. The most famous tin alloy is bronze. Roughly 5% tin smelted with 95% copper produces bronze. The development of bronze by primative humans was considered such an advancement that the era was called the "Bronze Age". Most solder is a combination of tin and lead. Another alloy of tin is pewter. Tin alloys had been used to make tin cans and tin roofs, but they are not used for those purposes too often now. Today, tin has significant use as a corrosion fighter in the protection of other metals and alloys and in use in the glass making industry as well as many other varied uses.

Native tin is found in placer deposits and in unusual igneous intrusions. Australia has the recognized type locality, but there is a report from Russia of an earlier find. Tin is too rare to be seen in typical rock shops, but laboratory specimens are being grown and put up for sale.

 

PHYSICAL CHARACTERISTICS:

  • Color is white to gray.
  • Luster is metallic.
  • Transparency: Specimens are opaque.
  • Crystal System is tetragonal (below 13.2 degrees C tin converts to isometric).
  • Crystal Habits include grains in placer deposits and lab grown specimens.
  • Cleavage is indistinct.
  • Hardness is 1.5 - 2.
  • Specific Gravity is 7.3 (heavy even for a metallic mineral).
  • Streak: white - gray.
  • Other Characteristics: Sectile.
  • Associated Minerals include native gold, native copper, stistaite, native aluminum and other rare native metals.
  • Notable Occurrences include the type locality of Aberfoil and Sam Rivers, Oban, New South Wales and Tasmania, Australia; Miass River, Southern Urals; Amur, Yakutia; Tolbachik, Kamchatka Peninsula and Aldan Shield, Siberia, Russia.
  • Best Field Indicators are color, brittleness, hardness, locality and density.
  •  

 

THE MINERAL TINAKSITE

  • Chemistry: K2Na(CaMn++)2(TiFe)Si6O17(OH)2, Potasium Sodium Calcium Manganese Titanium Iron Oxide Silicate Hydroxide.
  • Class: Silicates
  • Subclass: Inosilicates
  • Uses: Only as a mineral specimen.
  • Specimens
Tinaksite is named for some of the minerals in its composition (Titanium, Sodium, Potasium, Silicon).
Tinaksite is most commonly found as salmon colored fibrous aggregates in charoite specimens. It is often chatoyant, resulting in a very pretty specimen against the purple charoite.

PHYSICAL CHARACTERISTICS:

  • Color is pink, pale yellow or light brown.
  • Transparency: Specimens are transparent to translucent.
  • Luster: Vitreous.
  • Crystal System is triclinic.
  • Crystal Habit is fibrous or slender prisms (prismatic).
  • Hardness is 6.
  • Specific Gravity is 2.82 (average).
  • Streak is white.
  • Notable Occurrences are Murun, Siberia, Russia.

 

THE MINERAL TINCALCONITE

  • Chemistry: Na2B4O7 - 5H2 O, Hydrated Sodium Borate.
  • Class: Carbonates
  • Subclass: Borates
  • Uses: As an ore of boron and as a source of borax (a cleaning agent and useful industrial chemical)
  • Specimens
Tincalconite is a mineral that is closely related to and often intimately associated with the mineral borax. Most old mineral specimens of borax are chalky white due to a chemical reaction from dehydration. They have actually altered (at least on their surface and ultimately throughout) to the mineral tincalconite with the loss of water molecules. This kind of alteration from one mineral to another, can leave the shape of the original crystal intact. Mineralogists refer to this as a pseudomorph, or "false shape", because the tincalconite has the crystal shape of the predeceasing borax. Most all specimens of borax in museums and collections should technically be labeled "Tincalconite" or even more accurately "Tincalconite after Borax".
The formula of tincalconite can be written as: Na2B4O5(OH)4 - 3H2 O. This formula is technically identical to the formula that is generally used for tincalconite, Na2B4O7 - 5H2 O. The difference is in the number of oxygens, hydroxides and water molecules as shown below:
O2 + 2H2 O = (OH)4
The alternative formula reflects the ionic interaction of the hydroxides in the structure as opposed to a more passive role for the unbonded water molecules. The basic structure of tincalconite contains chains of interlocking BO2(OH) triangles and BO3(OH) tetrahedrons bonded to chains of sodium and water octahedrons.
Minerals that are the result of human intervention are sometimes not considered true minerals by mineral purists. Tincalconite, however, is not exclusively an alteration product of borax dehydration after the borax has been excavated, as some texts may lead people to believe. The mineral has been found as a naturally occurring secondary mineral at Searles Lake, California, the mineral's type locality. These specimens of cryptocrystalline aggregates are the result of dehydration of borax crystals that had been exposed to the dry air conditions at the site. In addition though, primary tincalconite crystals have been discovered there in drill cores forming well shaped di-rhombohedral pseudo-octahedral crystals. Primary means that the crystals were not the result of the alteration of other minerals.

PHYSICAL CHARACTERISTICS:

  • Color is white.
  • Luster is dull to earthy.
  • Transparency: Specimens are translucent to dull.
  • Crystal System is trigonal.
  • Crystal Habits include cryptocrystalline aggregates and as crusts. Rare primary, di-rhombohedral, pseudo-octahedral crystals have been found in drill cores from Searles Lake, California. Pseudomorphs of borax are blocky to prismatic crystals with a nearly square cross section.
  • Cleavage is not seen.
  • Fracture is earthy.
  • Hardness is probably about 1.
  • Specific Gravity is approximately 1.8 - 1.9 (very light)
  • Streak is white.
  • Associated Minerals are calcite, halite, hanksite, colemanite, ulexite and other borates especially borax.
  • Other Characteristics: A sweet alkaline taste and further dehydration may cause crumbling.
  • Notable Occurrences include Trona, Boron, Death Valley; Searles Lake, San Bernardino County and other California localities; arid regions of the Andes Mountains, South America; Turkey and Tibet.
  • Best Field Indicators are pseudomorphing habit, color, associations, locality, density and hardness.

 

THE MINERAL TITANIUM

  • Chemistry: Ti, Elemental Titanium
  • Class: Elements
  • Subclass: Native Metals
  • Uses: A white pigment (as oxide), medical devices, jewelry, aerospace alloys and military armor.
  • Specimens
Native titanium rarely occurs naturally in its elemental form, even though there are only six elements in the entire earth that are more abundant. It has been found in extremely high pressure metamorphic rocks and then only as inclusions. Titanium for industrial purposes is extracted primarily from rutile, ilmenite and leucoxene. Leucoxene is a mineraloid derived from weathered ilmenite.
Titanium was at one time a metal that had little use and basically no one knew what to do with it. Even as late as 1946 when the metal was finally shown to be capable of being produced commercially, it was considered a "laboratory curiosity". Since that time, titanium has been shown to be a strong aluminum-like metal; light weight, non-corrosive, able to withstand temperature extremes (especially its high melting point, 1800 degrees C) and it has good strength (as strong as steel and twice as strong as aluminum). Titanium alloys have found many applications in high tech airplanes, missiles, space vehicles and even in surgical implants.
Additionally, titanium dioxide TiO2, is a white pigment that is used more and more in paints as lead paint is discontinued due to health considerations. In fact, the largest percentage (up to 95%) of world wide use for titanium is for the production of this white pigment. The pigment has great luster, good endurance, high opacity (it hides whatever is under it, important for paint) and a pure white color. The pigment is also used to provide color for rubber, plastics, textiles, ink, cosmetics, leather, ceramics and paper. Titanium and titanium compounds have found uses in desalination plants, electrical components, glass products, artificial gemstones, jewelry and even as smoke screens. Ilmenite is mined in Australia, Brazil, Russia, Canada, Sri Lanka, Norway, China, South Africa, Thailand, India, Malaysia, Sierra Leone and the United States.
There are several common to relatively rare titanium minerals such as rutile, ilmenite, sphene, brookite, anatase, pyrophanite, osbornite, ecandrewsite, geikielite and perovskite to name a few. There is at least a small percentage of titanium in many many silicate and oxide minerals as titanium is actually quite a common element (9th most abundant in the Earth's crust). Of all of these minerals, only rutile, with a formula of TiO2, competes with ilmenite for dominance in the titanium source department. Even though rutile is the more common mineral and has a higher percentage of titanium in its formula, it is not concentrated in igneous deposits like ilmenite and is therefore less useful as an ore.
Titanium is three times stronger than steel, while weighing only 42% as much, making it an ideal strong, lightweight metal for structures such as airplanes and rockets. It is also chemically inert under normal conditions, enabling its use in medical implants such as pacemakers.
Titanium can be tarnished with heat or acids yielding uniquely colored, non-allergenic jewelry.

PHYSICAL CHARACTERISTICS:

  • Color is silver-gray often with a multi-colored iridescent tarnish.
  • Luster is metallic.
  • Transparency: Crystals are opaque.
  • Crystal System is hexagonal; 6/m 2/m 2/m. There is also an identified tetragonal variety.
  • Crystal Habits are limited to microscopic inclusions.
  • Cleavage is absent.
  • Hardness 4
  • Specific Gravity is 4.4 (light for metals).
  • Streak is black.
  • Associated Minerals include garnet and other ultrahigh pressure metamorphic minerals.
  • Notable Occurrences are limited to microscopic inclusions in coesite eclogites at Dabieshan, China and at Kamchatka and Amur, Russia.
  • Best Field Indicators: Rarity, color, luster and locality.

 

The Mineral TORBERNITE

Torbernite is a popular mineral among collectors who seek uranium bearing minerals. Its square tabular crystals are distinctive, but might remind someone of the mineral wulfenite, if not for the green color of tornernite. Autunite is a structurally related mineral that also forms square tabular crystals, but they are not typically solid green and autunite is fluorescent in UV light.
The structure of torbernite is composed of phosphate tetrahedrons linked to uranium-oxygen groups that form distorted octahedrons. The phosphates and uranium groups lie in sheets that are weakly held together by water molecules. This structure produces the tabular habit, the one perfect direction of cleavage and the relative softness.
Torbernite can lose water and convert to a different mineral called meta-torbernite of the meta-autunite/meta-torbernite group of minerals. The change to meta-torbernite will often produce a pseudomorph. A pseudomorph is generally an atom by atom replacement of one mineral's chemistry to form another mineral. The process leaves the crystal shape of the lost mineral intact. pseudomorph means false (psuedo) shape (morph). In this case, the conversion is not so dramatic since it involves only the lose of a few water molecules and therefore a good pseudomorph is likely. The conversion is irreversible and ongoing and all collection specimens of a certain age are almost certainly partially to totally converted.
The presence of torbernite crystal has been used by prospectors as an indicator of profitable uranium ore in the area. Fine torbernite specimens should be stored in a closed container to avoid water loss. 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:

  • Colors are various shades of dark to light green.
  • Luster is vitreous to pearly on the main pinacoid.
  • Transparency crystals can be transparent but more commonly are translucent to opaque.
  • Crystal System is tetragonal; 4/m 2/m 2/m
  • Crystal Habits include tabular square crystals dominated by two pinacoid faces. Crystals can look cubic, but the pearly luster only on the pinacoid faces gives the true symmetry away. Crystals can form in parallel growths giving a "stacked book" kind of look. Also as crusts, micaceous, foliated and scaly aggregates.
  • Cleavage is perfect in one direction.
  • Fracture is uneven.
  • Hardness is 2 - 2.5
  • Specific Gravity is approximately 3.2+ (slightly above average for translucent minerals)
  • Streak is a pale green.
  • Associated Minerals are autunite, uranophane, uranocircite, meta-torbernite, uraninite and other uranium minerals.
  • Other Characteristics: radioactive and cleavage sheets are not bendable but are in fact brittle.
  • Notable Occurences include Cornwall, England; Mitchell Co., North Carolina and Utah, USA; Shaba, Zaire; Germany and France.
  • Best Field Indicators are color, crystal habit, non-fluorescence, radioactivity, associations and brittle cleavage sheets.

 

THE MINERAL TREMOLITE

Tremolite is a relatively common mineral in some metamorphic rocks. It occurs from the conversion of dolomite, silica and water into tremolite, calcite and carbon dioxide by way of the following formula:
5CaMg(CO3)2 + 8SiO2 + H2O ------> Ca2Mg5Si8O22(OH)2 + 3CaCO3 + 7CO2
It belongs to a series with the minerals actinolite and ferro-actinolite. A series occurs when two or more ions can freely substitute between each other. In this case, when iron is predominant the mineral is ferro-actinolite and when magnesium is predominant the mineral is tremolite. Actinolite is the intermediate member and the most common followed by tremolite. Tremolite's formula is often written as the same as actinolite (with iron and magnesium), but specimens of tremolite can be found quite pure (that is, free of iron) and so here the formula reflects the pure end of the series. The entire series can be represented with the actinolite formula: Ca2(Mg, Fe)5Si8O22(OH)2.
Without the iron in the formula tremolite will have the typical creamy white color. With just a small amount of iron tremolite will be green. Increasing iron content will raise the specific gravity, index of refraction and darken the color.
A variety of tremolite is composed of microscopically fibrous crystals called asbestos. Other minerals also form asbestos such as serpentine and the other minerals of the series mentioned above. Serpentine asbestos is more widely used and of a better grade in general. Although asbestos has been shown to cause cancer in humans when inhaled in high enough concentrations, it still has many valuable applications. Asbestos is used for fire retardant materials and brake shoes and pads. Its prior use as insulation has been all but eliminated due to health concerns.
A variety of actinolite, nephrite, is one of the two minerals called jade. The other jade mineral is jadeite. Although nephrite is considered to be actinolite, the lighter shades of nephrite probably contain significant amounts of tremolite.
Another variety of tremolite is called "mountain leather" or "mountain cork" and is an oddity in the mineral world. The tremolite fibers form a felted mass that has all the appearances and feel of a piece of cloth. The mountain leather will even have attached calcite crystals that seem to be knitted in to the fabric. A violet variety of tremolite is called "hexagonite" and makes for a nice collection specimen with its attractive color and crystalline habit.
Tremolite is an important temperature indicator for petrologists. Because at high temperatures tremolite is unstable and will convert to diopside, CaMgSi2O6. The presence of only tremolite and no diopside indicates that the rock has not endured terribly high temperatures.
Tremolite can be a fun and very interesting mineral to collect.

PHYSICAL CHARACTERISTICS:

  • Color is usually white or gray but can be greenish, colorless, yellow and violet.
  • Luster is vitreous or silky to dull.
  • Transparency: Specimens are translucent to transparent.
  • Crystal System is monoclinic; 2/m
  • Crystal Habits include flattened prismatic and elongated crystals with a dome-like termination that is actually two of the four faces of a prism. Fibrous crystals form radial aggregates, masses and hair like clusters. Also as a felted mass (asbestos and "mountain leather").
  • Cleavage: is perfect in two directions at close to 60- and 120-degree angles (diamond-shaped).
  • Fracture is uneven.
  • Hardness is 5 - 6.
  • Specific Gravity is approximately 2.9 - 3.1 (very slightly above average for translucent minerals).
  • Streak is white.
  • Other Characteristics: Index of refraction is 1.60 - 1.63.
  • Associated Minerals are calcite, grossular, talc and serpentine.
  • Notable Occurrences include the area around Wilberforce, Ontario, Canada; De Kalb, St Lawrence Co., New York, California, Arizona and Canaan, Connecticut, USA; Tyrol and Piemonte, Italy; Tremola Valley, Switzerland (hence the name); Tanzania and Finland.
  • Best Field Indicators are fibrosity (asbestos), color, cleavage, crystal habit and hardness.

 

THE MINERAL TRIDYMITE

  • Chemistry: SiO2, Silicon Dioxide.
  • Class: Silicate
  • Group: Quartz.
  • Uses: As an indicator of high temperature crystallization and as mineral specimens.
  • Specimens
Tridymite is a polymorph of quartz, meaning that it is composed of the same chemistry, SiO2, but has a different structure. Both quartz and tridymite are polymorphs with all the members of the Quartz Group which also include coesite, cristobalite and stishovite.
At one time tridymite was considered rare, but that was before widespread testing of many different volcanic rocks turned out to contain lots of small to microscopic crystals of tridymite. Its wide spread distribution in certain types of rocks would require an abundance rating of at least common, although its identification is not easy.
Identification of tridymite without laboratory aid is limited to crystal habit and possibly index of refraction. What is needed to identify tridymite is a well formed crystal that shows the distinctive pseudohexagonal habit or the equally distinctive twinning. An index of refraction test would clinch the identification.
Tridymite has a higher temperature phase called beta tridymite. Most tridymite is believed to crystallize as beta tridymite which has an hexagonal symmetry and later as the crystal cools, it easily converts to tridymite. The conversion from beta tridymite to tridymite is so easy that the beta tridymite's hexagonal crystals are outwardly preserved in their original form. The beta tridymite has a higher symmetry than alpha tridymite or just tridymite. The interior structure is therefore not hexagonal anymore and thus the hexagonal looking crystals are called pseudomorphs or "false shape". Tridymite's actual symmetry was thought to be orthorhombic, but has since been found to be no higher in symmetry than monoclinic.
The presence of tridymite in a rock is helpful to petrologists (rock scientists) in determining the temperature of the rock at the time it crystallized. It will form from a melt at low pressures and at temperatures of approximately 870 degrees to 1470 degrees Celsius. Pressure and water content will vary this range, but it is usually a rather good indication of the temperature of the rock's crystallization. Below 870 degrees Celsius, beta quartz is stable and it will crystallize. Above 1470 degrees Celsius, cristobalite is stable and it will crystallize. Since a molten rock goes through various temperatures as it cools all three polymorphs could be present, confusing the issue.
Tridymite is only metastable at normal surface temperatures; meaning that, if it could, it would slowly convert to the quartz structure. But this is a slow and complicated process taking thousands of years if it happens at all. It is so slow a process mostly because the transformation involves the breaking of bonds and the rearrangement of atoms. Atoms of aluminum and sodium in the structure may help the stability of tridymite as well.

PHYSICAL CHARACTERISTICS:

  • Color is colorless or white.
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is monoclinic; 2/m or m (alpha tridymite) and hexagonal; 6/m 2/m 2/m (beta tridymite).
  • Crystal Habit includes the always small but sometimes well formed crystals that are pseudohexagonal being pseudomorphs of beta tridymite. The crystals are platy with a hexagonal cross-section. The more common habit is microscopic disseminated grains in volcanic rock. Twinning is common and often results in penetration twins that appear to have a second platy crystal growing into another crystal. The twins can look like a normal crystal that has been folded like a taco shell but with a sharp, not a rounded fold. By far, the more interesting twins are the six rayed trillings or "triplets" from where tridymite gets its name.
  • Cleavage is poor in three directions (prismatic).
  • Fracture is conchoidal.
  • Hardness is 7.
  • Specific Gravity is 2.27+ (below average for translucent minerals)
  • Streak is clear.
  • Other Characteristics: Refractive index is approximately 1.47
  • Associated Minerals include cristobalite, sanadine, hornblende, beta quartz, olivine, pseudobrookite and augite.
  • Notable Occurrences include Cerro San Cristobal, Pachuca, Mexico; San Juan Mountains and Yellowstone National Park, both in Colorado and Mt. Lassen, California, USA and Italy.
  • Best Field Indicators are crystal habit, environment of formation (mostly volcanic rocks), color and index of refraction.

THE MINERAL TRIPHYLITE

  • Chemistry: Li(Fe, Mn)PO4, Lithium Iron Manganese Phosphate.
  • Class: Phosphates
  • Uses: As a source of lithium and phosphorus and as mineral specimens.
  • Specimens
Triphylite is a rather scarce phosphate mineral. It forms a solid solution series with the often associated mineral lithiophilite. Lithiophilite's formula is Li(Mn, Fe)PO4 and differs from triphylite by being rich in manganese instead of iron. The structures of the two minerals are the same and therefore any differences in physical properties between the two would be related to the iron/manganese percentage. Lithiophilite is slightly less dense and is pinkish to greenish brown whereas triphylite's color tends toward blue and blue gray. The series is often called the "triphylite series" and the two minerals are often listed together in mineral field guides and reference manuals. Triphylite's name in Greek means "family of three" and is probably referring to the three ions: lithium, iron and manganese.
Although triphylite generally does not form good crystals, it does have a wonderful although indirect benefit to the mineral world. Triphylite is a primary phosphate mineral found in phosphatic pegmatites and pegmatitic dikes. It alters easily into other phosphate minerals, especially manganese phosphates. These rare phosphate minerals are usually brightly colored and make wonderful mineral specimens. Some mines have been made famous by their suites of unusual and beautiful secondary phosphate minerals such as eosphorite, reddingite, sicklerite, hureaulite, fairfieldite, dickinsonite, stewartite, vivianite, salmonsite, strengite, purpurite, heterosite, phosphoferrite, wolfeite, triploidite and fillowite to name a few. And where did these phosphates come from? They are the products of the alteration and/or weathering of triphylite, lithiophilite, amblygonite and a few other primary phosphate minerals. A lot of respect should be shown to triphylite and the other primary phosphate minerals for making these other minerals possible.

PHYSICAL CHARACTERISTICS:

  • Color is blue, gray-blue and gray-blue-green.
  • Luster is vitreous.
  • Transparency: Specimens are transparent to translucent.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits do not include well formed crystals because most crystals are embedded and appear as compact, cleavage masses and intergrown crystal clumps.
  • Cleavage is near perfect in one direction (basal) and imperfect in two directions (prismatic). All cleavages are at right angles to each other.
  • Fracture is uneven.
  • Hardness is variable from 4 - 5
  • Specific Gravity is approximately 3.58 (above average), but decreases with decreased iron content.
  • Streak is white to grayish-white.
  • Other Characteristics: When powdered and placed in a gas flame, it gives the flame a bright red color and this indicates the presence of lithium. Hyper-weathering produces a black stain of manganese oxides.
  • Associated Minerals include lepidolite, beryl, quartz, albite, lithiophilite, amblygonite, spodumene and various manganese oxides. Associated secondary phosphates include eosphorite, reddingite, sicklerite, salmonsite, strengite, purpurite, phosphoferrite, wolfeite, triploidite, hureaulite, fairfieldite, dickinsonite, stewartite, vivianite, heterosite and fillowite.
  • Notable Occurrences are widespread and include Verutrask, Sweden; Mangualde, Portugal; Bavaria, Germany; Buckfield, Poland; Karidid District, Namibia; Namaqualand, South Africa; the Buranga pegmatite, Rwanda; Yellowknife, Northwest Territories, Canada; Rajasthan, India; Rio Grande do Norte, Brazil and Pilbara District, Australia. In the United States localities include Pala District of San Diego County, California; Newry, Stoneham and Topsham, Maine; Palermo Quarry, North Groton, New Hampshire; Custer, South Dakota and Branchville, Fairfield County, Connecticut.
  • Best Field Indicators are color, associations, environment, cleavage and density.

 

THE MINERAL TRONA

  • Chemistry: Na3(HCO3)(CO3) - 2H2O , Hydrated Sodium Bicarbonate Carbonate.
  • Class: Carbonates
  • Uses: Only as mineral specimens.
  • Specimens
Trona is the type mineral so-to-speak for several sodium carbonates that form in non-marine evaporite deposits. Other sodium carbonates include gaylussite, natron, pirssonite, northupite, nahcolite and thermonatrite. Trona is probably the most common and well known of these minerals. They are all difficult to tell apart from each other except when good crystal form is present or when optical or X-ray techniques can be used. All are subject to dehydration and/or hydration to one degree or another and should be stored in sealed containers for this reason. All may form as efflorescent crusts on the walls of caves and mines or in soils in arid regions. Trona gets its name from a discarded Arabic word for native salt, "tron", which is derived from the word "natrun".

PHYSICAL CHARACTERISTICS:

  • Color is gray, colorless, white, pale brown or yellowish.
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is monoclinic; 2/m.
  • Crystal Habits include prismatic to blocky crystals, but usually massive, fibrous or columnar.
  • Cleavage is perfect in one direction and poor in two others.
  • Fracture is subconchoidal to uneven.
  • Hardness is 2.5 - 3.
  • Specific Gravity is 2.1 (well below average)
  • Streak is white.
  • Other Characteristics: Has an alkaline taste.
  • Associated Minerals include hanksite, gaylussite, halite, pirssonite, northupite, nahcolite, borax and calcite.
  • Notable Occurrences include Searles Lake, San Bernardino County; Borax Lake, Lake County; Owens Lake, Inyo County and Mono Lake, Mono County, California and Green River, Wyoming, USA; Iran; Tibet; Mont Saint-Hilaire, Quebec, Canada and Mongolia.
  • Best Field Indicators: environment of formation, color, cleavage, density, crystal habit, taste and locality.

 

TSAVORITE,

 a green gemstone variety of grossular garnet

VARIETY INFORMATION:

  • VARIETY OF: Grossular garnet, Ca3 Al2 Si3 O12.
  • USES: Gemstone.
  • COLOR: various shades of green.
  • INDEX OF REFRACTION: 1.73 - 1.75
  • HARDNESS: 6.5 - 7
  • CLEAVAGE: none
  • CRYSTAL SYSTEM: isometric
  • SPECIMENS
Tsavorite is one of the gem varieties of the garnet mineral called grossular. The more common gem variety of grossular is called hessonite. Gem quality tsavorite is found at Tsavo, Kenya. The green color is caused by trace amounts of vanadium. Tsavorite is not the only green garnet. Uvarovite is almost never used as a gemstone, but the green andradite garnet variety called demantoid are also cut for gems. Distinguishing them can be difficult, but experienced gem dealers are capable of doing so.

 

THE MINERAL TSUMCORITE

  • Chemistry: Pb(Zn, Fe)2(AsO4)2 - H2O, Hydrated Lead Zinc Iron Arsenate
  • Class: Phosphates
  • Subclass: Arsenates
  • Uses: Only as mineral specimens.
  • Specimens
Tsumcorite is another mineral that honors the great mineral site of Tsumeb, Namibia. Tsumcorite was first discovered there and is named in its honor. Tsumebite is a phosphate mineral that was also found there and is likewise named for the locality. Tsumcorite forms in oxidation zone of the weathered ore body and is the product of secondary crystallization. As a very rare mineral, tsumcorite is too easy a mineral to identify. Its distinctive color, uncommon yellow streak and a very high density make it very difficult to mistake. The much more common mimetite, which is associated with tsumcorite, is the only thing close, but has a distinctly different crystal habit.

PHYSICAL CHARACTERISTICS:

  • Color is reddish brown to yellowish brown or orange.
  • Luster is vitreous.
  • Transparency: Crystals are translucent.
  • Crystal System is monoclinic.
  • Crystal Habits include platy or prismatic to acicular crystals and radiating fibrous masses and crusts.
  • Cleavage is not observed.
  • Fracture is uneven.
  • Hardness is 4.5
  • Specific Gravity is approximately 5.2 (rather heavy for translucent minerals).
  • Streak is pale yellow.
  • Associated Minerals are malachite, cerussite, mimetite and other secondary arsenate minerals.
  • Notable Occurrence is limited to Tsumeb, Namibia.
  • Best Field Indicators are color, crystal habit, density, yellow streak and locality.

 

THE MINERAL TSUMEBITE

  • Chemistry: Pb2Cu(PO4)(SO4)OH , Lead Copper Phosphate Sulfate Hydroxide
  • Class: Phosphates
  • Uses: only as a mineral specimen.
  • Specimens
Tsumebite forms good, colorful specimens and is a popular collection mineral, although quite rare. It is closely related to its cousin, arsentsumebite. The two minerals are in a series in which the arsenate ion group in arsentsumebite is replaced by a phosphate ion group in tsumebite. The two differ only slightly mostly because the structure is the same in the two minerals. Both are formed in the oxidation zone of lead-copper ore deposits.
Both minerals are unusual in that they have two ion groups instead of the usual one in most minerals. It the case of tsumebite, it has a phosphate ion group and a sulfate ion group. Mineralogists prefer to classify it as a phosphate because the phosphate ion group has a higher negative charge (-3) than the sulfate group (-2).

PHYSICAL CHARACTERISTICS:

  • Color is emerald green and yellow-green.
  • Luster is vitreous.
  • Transparency crystals are transparent to translucent.
  • Crystal System is monoclinic.
  • Crystal Habits include tabular crystals that can form twinned trillings and also as crusts and spherules.
  • Cleavage: None.
  • Fracture: Uneven.
  • Hardness is 3.5
  • Specific Gravity is approximately 6.2 (heavy for translucent minerals)
  • Streak is green.
  • Associated Minerals include azurite, wulfenite, mimetite, cerussite and smithsonite.
  • Notable Occurrences are limited to Tsumeb, Namibia and Morenci, Arizona, USA.
  • Best Field Indicators are crystal habit, locality, associations, density and color.

 

THE MINERAL TURQUOISE

  • Chemistry: CuAl6(PO4)4(OH)8*5(H2O), Hydrated Copper Aluminum Phosphate
  • Class: Phosphates
  • Uses: as an ornamental stone for carving and jewelry.
  • Specimens
Turquoise is a valuable mineral and is possibly the most valuable, non-transparent mineral in the jewelry trade. It has been mined for eons since at least 6000 BC. by early Egyptians. Its history also includes beautiful ornamental creations by Native Americans and Persians. Its popularity is still quite strong today. Although crystals of any size are rare, some small crystals have been found in Virginia and elsewhere. Most specimens are cryptocrystalline, meaning that the crystals could only be seen by a microscope. The finest turquoise comes from Iran but is challenged by some southwestern United States specimens. Turquoise is often imitated by "fakes", such as the mineral chrysocolla, and poorer turquoise specimens are often dyed or color stabilized with coatings of various resins. The name comes from a french word which means stone of Turkey, from where Persian material passed on its way to Europe.

PHYSICAL CHARACTERISTICS:

  • Color is of course, turquoise, but this color actually varies from greenish blue to sky blue shades.
  • Luster is dull to waxy, vitreous in macro-crystals.
  • Transparency specimens are opaque.
  • Crystal System is triclinic; bar 1
  • Crystal Habits include crystals rarely large enough to see, usually massive, cryptocrystalline forms as nodules and veinlets.
  • Cleavage is perfect in two direction, but is not often seen.
  • Fracture is conchoidal and smooth.
  • Hardness is 5 - 6
  • Specific Gravity is approximately 2.6 - 2.8 (average)
  • Streak is white with a greenish tint.
  • Associated Minerals are pyrite. limonite. quartz and clays.
  • Other Characteristics: color can change with exposure to skin oils.
  • Notable Occurances include Arizona and New Mexico, USA; Australia; Iran; Afghanistan and other locallities in the Middle East.

The Mineral TYUYAMUNITE

  • Chemistry: Ca(UO2)2(VO4)2- 5-8H2O , Hydrated Calcium Uranyl Vanadate.
  • Class: Phosphates
  • Group: Vanadium Oxysalt
  • Uses: a very minor ore of uranium and as mineral specimens
  • Specimens
Tyuyamunite is a rare uranium mineral that is named for the type locality from where it was first described, Tyuya Muyun, Ferghana, Uzbekistan. Tyuyamunite is closely related to carnotite, K2(UO2)2(VO4)2- 1-3H2O. The chemistries are very similar with potassium replacing calcium and a different percentage of water, however the structures are slightly different as tyuyamunite is orthorhombic and carnotite is monoclinic. The two minerals are often found together and are essentially indistiguishable by ordinary methods. Meteoric oxygenated waters dissolve the uranium from primary uranium minerals and the uranium is later deposited in reducing enviroments more favorable to the formation of carnotite and tyuyamunite. Since many deposits in sandstones are associated with petrified trees and other fossils, it is reasonable to assume that the decaying material helped produce the required reducing enviroment. Tyuyamunite is a rare and interesting uranium mineral. Remember, this is also a radioactive mineral and should be stored away from other minerals that are affected by radioactivity and human exposure should always be limited.

PHYSICAL CHARACTERISTICS:

  • Colors are various shades of yellow, commonly greenish yellow.
  • Luster is vitreous or waxy to dull or earthy.
  • Transparency crystals are translucent to opaque.
  • Crystal System is orthorhombic; possibly 2/m 2/m 2/m
  • Crystal Habits include crusts, earthy masses, foliated and scaly aggregates.
  • Cleavage is perfect in one direction, micaceous.
  • Fracture is uneven.
  • Hardness is 2.
  • Specific Gravity is approximately 3.4 - 4 (above average for translucent minerals), higher gravity with lower water content.
  • Streak is yellow.
  • Associated Minerals include carnotite and other uranium and vanadium minerals in sandstones.
  • Other Characteristics: radioactive and some specimens are weakly fluorescent yellow to yellow-green.
  • Notable Occurrences include Tyuya Muyun, Ferghana, Uzbekistan; Wyoming, Colorado, Arizona, Nevada, Utah, New Mexico and Texas, USA.
  • Best Field Indicators are color, habit, fluorescence if present, radioactivity and associations.

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