7 Photos
Ankerite
Chemical Formula	Ca(Fe,Mg,Mn)(CO3)2
Species	Carbonates
Crystal System	Trigonal
Mohs Scale	3-4
Specific Gravity	2.93-3.10
Color	Brown, yellow, white
Streak	White
Luster	Vitreous, Pearly
Refractive Index	n = 1.690 - 1.750 n = 1.510 - 1.548
Diaphaneity	Transparent, Translucent
Cleavage	PerfectPerfect on
Fracture	Sub-Conchoidal
Crystal Habit：Chrystals rhombohedral with curved faces; columnar, stalactitic, granular, massive
Geological Setting：Low grade metamorphism of ironstones and banded iron formation.

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. Forms series with dolomite and kutnohorite.

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 color is white, grey or reddish to yellowish brown.

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. 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.

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