The Mineral CHALCOSIDERITE

Chemistry: CuFe6(PO4)4(OH)8 - 4H2O, Hydrated Copper Iron Phosphate Hydroxide.
Class: Phosphates
Group: Turquoise
Uses: Only as mineral specimens.
Specimens

Chalcosiderite is a rare copper phosphate mineral. It is another rare mineral from the classic localities' of Cornwall, England. Its typical bright, dark green color is attractive and diagnostic.

Chalcosiderite is in a solid solution series with the mineral turquoise. A solid solution series occurs when more than one element can occupy the same space in a mineral's structure and freely substitute for each other. Chalcosiderite and turquoise have the same structure, just slightly different chemistries. Turquoise's formula is CuAl6(PO4)4(OH)8 - 4H2O and is the aluminum rich end member of the series. Chalcosiderite is the iron rich end member and it is the coloring effects of the iron that produces the darker color for chalcosiderite as opposed to turquoise's lighter blue-green.

PHYSICAL CHARACTERISTICS:

Color is green.
Luster is vitreous.
Transparency: Specimens are translucent to less often transparent.
Crystal System is triclinic.
Crystal Habits include tiny prismatic to tabular crystals and crusts.
Cleavage is perfect.
Fracture is uneven.
Hardness is 4.5
Specific Gravity is approximately 3.2 (slightly above average).
Streak is green.
Associated Minerals include malachite, libethenite, olivenite and limonite.
Notable Occurrences include the Wheal Phoenix Mine, Cornwall, England; Seigen, Westphalia, Germany and Cochise County, Arizona, USA.
Best Field Indicators are color, locality, crystal habit, associations and perfect cleavage.