Faustite

The IMA-approved mineral faustite^[1] is a member of the triclinic turquoise group of hydrous phosphates with the chemical composition ZnAl₆(PO₄)₄(OH)₈·4H₂O. It is named after the American mineralogist and petrologist Dr. George Tobias Faust, who workes with the U.S. Geological Survey (USGS).^[2]

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. It may be presented as a turquoise imitation and also be treated with stabilizers for jewelry making.

• IMA Database of Mineral Properties - Faustite
• Mindat.org - Faustite
• Webmineral.com - Faustite Mineral Data