ankerite

{{Infobox mineral | name = Ankerite | boxwidth = | boxbgcolor = | image = Ankérite (Grandfontaine)-Musée de minéralogie de Strasbourg.jpg | imagesize = 260px | alt = | caption = | category = Carbonate mineral | formula = |IMAsymbol=Ank | molweight = | strunz = 5.AB.10 | dana = | system = Trigonal | class = Rhombohedral () H–M symbol: () | symmetry = R | unit cell = a = 4.8312(2) c = 16.1663(3) [Å]; Z = 3 | color = Brown, yellow, white | colour = | habit = Chrystals rhombohedral with curved faces; columnar, stalactitic, granular, massive | twinning = Simple t {0001}, {100}. {110} | cleavage = Perfect on {101} | fracture = Subconchoidal | tenacity = Brittle | mohs = 3.5–4.0 | luster = Vitreous to pearly | streak = White | diaphaneity = Translucent to transparent | gravity = 2.93–3.10 | density = | polish = | opticalprop = Uniaxial (−) | refractive = nω = 1.690–1.750 nε = 1.510–1.548 | birefringence = δ = 0.180–0.202 | pleochroism = | 2V = | dispersion = Strong | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = | other = | prop1 = | prop1text = | references = }} Ankerite, also known as brown spar () is a calcium, iron, magnesium, manganese carbonate mineral of the group of rhombohedral carbonates with the chemical formula . In composition it is closely related to dolomite, but differs from this in having magnesium replaced by varying amounts of iron(II) and manganese. It forms a series with dolomite and kutnohorite.

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