Chalcosiderite

Chalcosiderite - A Rare Cousin of Turquoise

One of our all time favorite gems is Chalcociderite.  This rare natural gem is a rare cousin of Turquoise.This gem is stunningly beautiful and comes all sorts of colors from tan to green to orange, white and yellow.  Often called Turquoise in the past it has come into its own in recent years in the jewelry world. With the growing popularity of Variscite, Chalcosiderite has also moved up in the gem world as it should have long ago.  Infact, most of what is being called Nevada Variscite is actually Chalcosiderite.

Chalcosiderite is beloved for its wonderful colors, hardness and matrix patterns.  Most of the high grade Chalcosiderite is features stunning spiderweb matrix.  Many good examples come from Nevada.  Such mines as the famous Damele mine, New Lander mine, and the Colorback mine to name a few greatly added to the popularity of high grade Chalcociderite.  Most of this material was sold early on as Turquoise.  Almost all of this material features gorgeous black spiderweb matrix.

Recently several old mines have been re-discovered and new mines found which have deposits of Chalcosiderite and Variscite. A few of these which have been gaining popularity are the Tortoise, Peacock, Miss Moffet, Seven Dwarfs, Poseidon, and Desert Bloom mines in Nevada and the Snowville mine in Utah, just to name a few.

Composition: 

Structure and Associated Minerals:There is a complete solution which exists between Chalcosiderite, CuFe₆ (PO₄)₄ (OH)₈:4H₂O, and turquoise CuAl₆ (PO₄)₄(OH)₈:4H₂O. Because of this, aluminum may partly substitute for iron in the mineral's crystal structure. In places like Lander County Nevada, Chalcosiderite and turquoise also occur together in the same general area.

Identification and Diagnostics:Gives a positive test for copper, iron and phosphates, but exact determinations between turquoise and chalcosiderite may require a chemical analysis of the mineral make up.

Occurrence, Localities and Origins:

A rare copper-iron secondary phosphate. It occurs only in a few places in the US, where it is associated with the oxidized zones of some copper deposits. In Lander County, Nevada it occurs at the Damale mine where it is found as emerald green nodules in association with variscite and faustite. It is also found at the Lander Ranch mine near Tenabo as well as the mines above.