1911 Encyclopædia Britannica/Ankerite

by Leonard James Spencer

ANKERITE, a member of the mineral group of rhombohedral carbonates. In composition it is closely related to dolomite, but differs from this in having magnesia replaced by varying amounts of ferrous and manganous oxides, the general formula being Ca(Mg, Fe, Mn)(CO₃)₂. Normal ankerite is Ca₂MgFe(CO₃)₄. The crystallographic and physical characters resemble those of dolomite and chalybite. The angle between the perfect rhombohedral cleavages is 73° 48′, the hardness 31/2 to 4, and the specific gravity 2·9 to 3·1; but these will vary slightly with the chemical composition. The colour is white, grey or reddish.

Ankerite occurs with chalybite in deposits of iron-ore. It is one of the minerals of the dolomite-chalybite series, to which the terms brown-spar, pearl-spar and bitter-spar are loosely applied. It was first recognized as a distinct species by W. von Haidinger in 1825, and named by him after M. J. Anker of Styria.  (L. J. S.)