Ankerite occurs with siderite in metamorphosed ironstones and sedimentary banded iron formations. It also occurs in carbonatites. In sediments it occurs as authigenic, diagenetic minerals and as a product of hydrothermal deposition.[1] 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.[2]