Tuesday, August 23, 2011

Mineral Q


Additional variety specimens include:

Quartz is the most common mineral on the face of the Earth. It is found in nearly every geological environment and is at least a component of almost every rock type. It frequently is the primary mineral, >98%. It is also the most varied in terms of varieties, colors and forms. This variety comes about because of the abundance and widespread distribution of quartz. A collector could easily have hundreds of quartz specimens and not have two that are the same due to the many broad catagories. The specimens could be separated by answers to the following questions: color?, shade?, pyramidal?, prismatic?, druzy?, twinned?, sceptered?, phantomed?, included?, tapered?, coated?, microcrystalline?, stalactitic?, concretionary?, geoidal?, banded?, etc. Multiple combinations of these could produce hundreds of unique possibilities.

 Some macrocrystalline (large crystal) varieties are well known and popular as ornamental stone and as gemstones.

  • Amethyst is the purple gemstone variety.
  • Citrine is a yellow to orange gemstone variety that is rare in nature but is often created by heating Amethyst.
  • Milky Quartz is the cloudy white variety.
  • Rock crystal is the clear variety that is also used as a gemstone.
  • Rose quartz is a pink to reddish pink variety.
  • Smoky quartz is the brown to gray variety.
Cryptocrystalline (crystals too small to be seen even by a microscope) varieties are also used as semi-precious stones and for ornamental purposes. These varieties are divided more by character than by color. Chalcedony or agate is divided into innumeral types that have been named for locally common varieties. Some of the more beautiful types have retained their names on a world-wide basis while other names have faded into obscurity. Some of the more common of these types are chrysoprase (a pure green agate), sard (a yellow to brown agate), sardonyx (banded sard), onyx (black and white agate), carnelian (a yellow to orange agate), flint (a colorful and microscopically fibrous form), jasper (a colorful impure agate) and bloodstone (a green with red speckled agate).

Quartz is not the only mineral composed of SiO2. There are no less than eight other known structures that are composed of SiO2. These other substances and quartz are polymorphs of silicon dioxide and belong to an informal group called the Quartz Group or Silica Group. All members of this group, except quartz, are uncommon to extemely rare on the surface of the earth and are stable only under high temperatures and high pressures or both. These minerals have their own unique structures although they share the same chemistry, hence the term polymorph, which means many forms.

Quartz has a unique structure. Actually, there is another mineral that shares quartz's structure, and it is not even a silicate. It is a rare phosphate named berlinite, AlPO4, that is isostructural with quartz. The structure of quartz involves corkscrewing (helix) chains of silicon tetrahedrons. The corkscrew takes four tetrahedrons in order to repeat itself, or three turns. Each tetrahedron is essentially rotated 120 degrees. The chains are aligned along the C axis of the crystal and interconnected to two other chains at each tetrahedron making quartz a true tectosilicate. This structure is not like the structure of the chain silicates or inosilicates whose silicate tetrahedronal chains are not directly connected to each other. The structure of quartz helps explain many of its physical attributes.

For one, the helix makes three turns and this helps produce the trigonal symmetry of quartz. Likewise a helix or corkscrew lacks mirror planes of symmetry as does quartz. The corkscrew structure would also disrupt any cleavage which requires a plane of weakness not found in quartz and breakage would result in the curved fracture, conchoidal, that is found in quartz. Quartz can also have left and right handed crystals just as a corkscrew can screw in a left handed way or in a right handed way. There are even some very difficult to identify crystals of quartz that are twinned with alternating one sixths of the crystal being right handed and then left handed.

Quartz is a fun mineral to collect. Its abundance on the Earth's surface is incredible and produces some wonderful varieties that don't even look like the same mineral. A collector must always be up on the many varieties of quartz and it sometimes embarrasses a collector to have collected too many specimens of such a common mineral. But nearly all collectors concede that you can never really have enough quartz specimens.




  • Color is as variable as the spectrum, but clear quartz is by far the most common color followed by white or cloudy (milky quartz). Purple (Amethyst), pink (Rose Quartz), gray or brown to black (Smoky Quartz) are also common. Cryptocrystalline varieties can be multicolored.
  • Luster is glassy to vitreous as crystals, while cryptocrystalline forms are usually waxy to dull but can be vitreous.
  • Transparency: Crystals are transparent to translucent, cryptocrystalline forms can be translucent or opaque.
  • Crystal System is trigonal; 3 2.
  • Crystal Habits are again widely variable but the most common habit is hexagonal prisms terminated with a six sided pyramid (actually two rhombohedrons). Three of the six sides of the pyramid may dominate causing the pyramid to be or look three sided. Left and right handed crystals are possible and identifiable only if minor trigonal pyramidal faces are present. Druse forms (crystal lined rock with just the pyramids showing) are also common. Massive forms can be just about any type but common forms include botryoidal, globular, stalactitic, crusts of agate such as lining the interior of a geode and many many more.
  • Cleavage is very weak in three directions (rhombohedral).
  • Fracture is conchoidal.
  • Hardness is 7, less in cryptocrystalline forms.
  • Specific Gravity is 2.65 or less if cryptocrystalline. (average)
  • Streak is white.
  • Other Characteristics: Striations on prism faces run perpendicular to C axis, piezoelectric (see tourmaline) and index of refraction is 1.55.
  • Associated Minerals are numerous and varied but here are some of the more classic associations of quartz (although any list of associated minerals of quartz is only a partial list): amazonite a variety of microcline, tourmalines especially elbaite, wolframite, pyrite, rutile, zeolites, fluorite, calcite, gold, muscovite, topaz, beryl, hematite and spodumene.
  • Notable Occurrences of amethyst are Brazil, Uraguay, Mexico, Russia, Thunder Bay area of Canada, and some locallities in the USA. For Smoky Quartz; Brazil, Colorado, Scotland, Swiss Alps among many others. Rose Quartz is also wide spread but large quantities come from brazil as do the only large find of Rose Quartz prisms. Natural citrine is found with many amethyst deposits but in very rare quantities. Fine examples of Rock crystal come from Brazil (again), Arkansas, many locallities in Africa, etc. Fine Agates are found in, of course, Brazil, Lake Superior region, Montana, Mexico and Germany.
  • Best Field Indicators are first the fact that it is very common (always assume transparent clear crystals may be quartz), crystal habit, hardness, striations, good conchoidal fracture and lack of good cleavage.







  • Chemistry: Zn8Cu4(TeO3)3(OH)18, Zinc Copper Tellurite Hydroxide
  • Class: Sulfates
  • Subclass: Tellurites
  • Uses: A very minor ore of tellurium and as mineral specimens.
  • Specimens

Quetzalcoatlite is a very rare and an unusual mineral from Mexico. The bright blue translucent mineral is named for the Aztec God: Quetzalcoatl (which means "Feathered Serpent"). Another Mexican mineral named for a God is tlalocite which is named for the Aztec Rain God: Tlaloc. Some other minerals named for gods include aegirine, after Aegir (the Scandinavian god of the sea) and neptunite, after Neptune (the Roman god of the sea). There are no hard and fast rules for naming minerals, except that the first name is the official name (generally). Minerals are named after their areas of discovery (or type locality, see franklinite); their discover or a scientist of noteworthy proportions (see smithsonite or weloganite); their typical crystal forms (see tetrahedrite) and minerals have even been named for their chemistries (see cavansite). But few minerals have been named after gods.

Quetzalcoatlite is one of several different, but all rare tellurium minerals that come from the Moctezuma area of Sonora, Mexico. There are three formerly prolific mines from this area that have provided science with many new tellurium minerals. They are the Bambollita Mine, the Moctezuma Mine and the San Miguel Mine. The Bambollita Mine has also been known as the La Oriental Mine and is the type locality for Quetzalcoatlite. The Moctezuma Mine has also been known as the La Bambolla Mine; which is often confused with the Bambollita Mine, as one might imagine. Below is an incomplete list of tellurium minerals from the Moctezuma area.

Tellurium Minerals From The Moctezuma Area Mines:

Lead Telluride
Calcium Tellurium
Carbonate Oxide
Copper Selenide Telluride
Tellurium Oxide
Silver Antimony Arsenic
Telluride Sulfide
Hydrated Iron Tellurite Sulfate
Hydrated Lead Iron Manganese
Tellurium Aluminum Silicate Hydroxide
Zinc Copper Tellurite Hydroxide
Calcium Tellurite
Uranyl Tellurite
Silver Telluride Sulfide
Hydrated Iron Tellurite Hydroxide
Hydrated Lead Copper Tellurite
Manganese Tellurite
Uranium Tellurite
Tellurium Oxide
Hydrated Iron Tellurate
native Te
Calcium Manganese Zinc Tellurite
Bismuth Telluride Sulfide
Hydrated Iron Tellurite
Hydrated Copper Zinc
Tellurate Chloride Hydroxide
Hydrated Iron Lead Tellurate Hydroxide
Calcium Lead Copper
Zinc Sulfate Tellurate
Iron Tellurite Hydroxide
Copper Tellurate Hydroxide
Lead Uranyl Tellurite
Hydrated Magnesium
Zinc Iron Tellurite



  • Color is a bright blue.
  • Luster is vitreous.
  • Transparency: Crystals are translucent.
  • Crystal System is hexagonal; 6 2 2.
  • Crystal Habits include small granular crystals.
  • Cleavage is good.
  • Hardness is 3.
  • Specific Gravity is approximately 6.1 (very heavy for translucent minerals)
  • Streak is white.
  • Associated Minerals include tellurium minerals such as dugganite and khinite and various other tellurates and tellurites Also associated with gold.
  • Notable Occurrences are limted to the Bambollita Mine (La Oriental), Sierra La Huerta, Moctezuma, Sonora, Mexico and at least one specimen was found at the Old Guard Mine, Tombstone, Arizona.
  • Best Field Indicators are locality, color, density and cleavage.

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