The
IMA approved mineral faustite,
named after the American mineralogist and petrologist with the U.S. Geological Survey (
USGS
The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...
) Dr. George Tobias Faust, is a member of the
triclinic
180px, Triclinic (a ≠ b ≠ c and α ≠ β ≠ γ )
In crystallography, the triclinic (or anorthic) crystal system is one of the 7 crystal systems. A crystal system is described by three basis vectors. In the triclinic system, the crystal i ...
turquoise group of hydrous
phosphates
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid .
The phosphate or orthophosphate ion is derived from ph ...
with the following chemical composition:
ZnAl6(PO4)4(OH)8·4H2O
Some divalent
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish ...
generally replaces the
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic t ...
position. Faustite is the zinc rich analogue of
turquoise
Turquoise is an opaque, blue-to-green mineral that is a hydrated phosphate of copper and aluminium, with the chemical formula . It is rare and valuable in finer grades and has been prized as a gemstone and ornamental stone for thousands of y ...
having almost four times as much zinc than copper in its crystal structure.
Trivalent (
ferric
In chemistry, iron(III) refers to the element iron in its +3 oxidation state. In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe3+.
The adjective ferric or the prefix ferri- is often used to s ...
) iron may replace some of the aluminum. Minor amounts of calcium may also be present. It has a hardness of 4.5 - 5.5 on the
Mohs scale of mineral hardness
The Mohs scale of mineral hardness () is a Qualitative property, qualitative ordinal scale, from 1 to 10, characterizing scratch hardness, scratch resistance of various minerals through the ability of harder material to scratch softer material.
...
and aside from having a slightly lower hardness, it may be difficult to distinguish it from turquoise in hand specimens.
Faustite has a blue-green to apple green color in polished cabochons, and may be presented as a turquoise imitation, and it may also be treated with stabilizers for jewelry making.
References
{{Reflist
IMA Database of Mineral Properties - FaustiteWebmineral.com - Faustite Mineral Data
Phosphate minerals
Triclinic minerals
Minerals in space group 2