Bitter spar

Ankerite

[ang-kuh-rahyt]
Ankerite is a calcium, iron, magnesium, manganese carbonate mineral of the group of rhombohedral carbonates with formula: Ca(Fe, Mg, Mn)(CO3)2. In composition it is closely related to dolomite, but differs from this in having magnesium replaced by varying amounts of iron(II) and manganese.

The crystallographic and physical characters resemble those of dolomite and siderite. The angle between the perfect rhombohedral cleavages is 73° 48', the hardness is 3.5 to 4, and the specific gravity is 2.9 to 3.1. The colour is white, grey or reddish to yellowish brown. The variety called normal ankerite is Ca2MgFe(CO3)4.

Ankerite occurs with siderite in deposits of iron-ore. It is one of the minerals of the dolomite-siderite series, to which the terms brown-spar, pearl-spar and bitter-spar have been historically loosely applied.

Ankerite can result from hydrothermal or direct groundwater precipitation. It can also be the result of metamorphic recrystallization of iron-rich sedimentary rocks. It is often found as a gangue mineral associated with gold and a variety of sulfide minerals in ore deposits.

It was first recognized as a distinct species by W. von Haidinger in 1825, and named by him after Matthias Joseph Anker (1771-1843) of Styria, an Austrian mineralogist.

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