Faustite
The IMA approved mineral faustite,[1] named after the American mineralogist and petrologist with the U.S. Geological Survey (USGS) Dr. George Tobias Faust,[2] is a member of the triclinic turquoise group of hydrous phosphates with the following chemical composition:
ZnAl6(PO4)4(OH)8·4H2O
Some divalent copper generally replaces the zinc position. Faustite is the zinc rich analogue of turquoise having almost four times as much zinc than copper in its crystal structure.[3] Trivalent (ferric) 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 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.
