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The Calcite Group of Minerals


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Calcite (CaCO3)

Gaspeite ({Ni, Mg, Fe}CO3)

Magnesite (MgCO3)

Otavite (CdCO3)

Rhodochrosite (MnCO3)

Siderite (FeCO3)

Smithsonite (ZnCO3)

Sphaerocobaltite (CoCO3)

COMPOSITION OF THE CALCITE GROUP:
CaCO3 (calcite), MgCO8 (magnesite), and FeCO3 (siderite). These Mineral names have also sometimes been given to intermediate members of the group. Because Pure calcium, iron, or magnesium carbonates are uncommon, but we can usually say that a specimen has predominantly one or another composition and, hence, give it a name which is close enough. However, in recent years analyses show that all possible combinations of these elements with manganese, zinc, and cobalt cannot exist in nature, and the old simple explanation is no longer accurate. Two other calcite group members are rhodochrosite and smithsonite. All of the members of this group belong to the rhombohedral division of the hexagonal system. All have excellent rhombohedral cleavage. Crystals and crystalline masses are common. All have strong double refraction (best shown by the doubling of lines or dots seen through a clear cleavage of "Iceland spar".

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