The Turquoise Mineral Group - What's the difference between Turquoise, Variscite, Chalcosiderite, and Faustite?
There is much confusion surrounding the subject of Turquoise and those minerals that form under similar conditions. This post is an attempt to shed some light on the unique chemical makeup of Turquoise and its closely related siblings.
The Turquoise Mineral Group:
Turquoise is formed by a complex combination of aluminum, copper, phosphorus, water, and other local ingredients that may change the color or add matrix (host rock). Turquoise is
found at elevations between 3,000 - 8,500 feet and typically in dry, arid climates. Other, very similar minerals also form under these conditions- and five of these are classified under the Turquoise Mineral Group.
The turquoise mineral group includes: Turquoise, Faustite, Chalcosiderite, Aheylite, and Planerite.
For simplicity sake, most artists and galleries working with these stones classify all the members of the turquoise mineral group as "Turquoise".
They are extremely similar stones, made different by the levels of zinc, iron, and copper present in the ground where they form. But they all fall under the umbrella of the Turquoise Mineral Group.
Chalcosiderite:
Other than Turquoise, two of the most commonly seen members of the turquoise group include Chalcosiderite and Faustite. Chalcosiderite replaces iron in its chemical formula, instead of the aluminum in Turquoise. However some Chalcosiderite contains both iron and aluminum and can be difficult to chemically distinguish from Turquoise. Some famous mines that produce this form of Chalcosiderite include the New Lander, Damele, and Peacock mines.
Peacock Turquoise Necklace
Faustite:
Faustite replaces zinc in its chemical formula, instead of the aluminum in Turquoise. However, once again, Faustite can contain both zinc and aluminum and becomes difficult to distinguish from turquoise. Famous mines that produce this form of Faustite include the Carico Lake and Orvil Jack mines.
Variscite:
While both Turquoise and Variscite form under similar conditions, we identify them as separate stones on our site. Turquoise is a hydrous phosphate of aluminum and copper and Variscite is considered a hydrated aluminum phosphate. Here's their chemical makeup:
Variscite: AlPO4•2H2O
Turquoise: CuAl6(PO4)4(OH8)•4H2O
For those of us without degrees in Geology, those equations look like Greek. To put it in layman terms, Variscite is a brighter green and typically has less complex matrix than its sister Turquoise.
Variscite is usually seen to be on its own- it’s a brighter green color- and we try to identify it as its own mineral. This can get complicated too however, because once again, certain veins can produce both Variscite and Turquoise (or a blend) in the same deposit. One mine that can produce both Variscite and Turquoise is the Broken Arrow mine in Nevada.
I really enjoyed this explanation. Thank you for making it available!
Nicely written article with mineralogy background.
Thanks. This is just the kind of information I crave. I collect and love SW jewelry and fetish carvings and I love your site. One of my favorite pendants I got from you. It is a two-sided maiden pendant by Rita Begay.
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