Ankerite

{{Short description|Calcium, iron, magnesium, manganese carbonate mineral}}

{{Infobox mineral

| name = Ankerite

| boxwidth =

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| image = Ankérite (Grandfontaine)-Musée de minéralogie de Strasbourg.jpg

| imagesize = 260px

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| category = Carbonate mineral

| formula = {{chem2|Ca(Fe,Mg,Mn)(CO3)2}}

|IMAsymbol=Ank{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}

| molweight =

| strunz = 5.AB.10

| dana =

| system = Trigonal

| class = Rhombohedral ({{overline|3}})
H–M symbol: ({{overline|3}})

| symmetry = R{{overline|3}}

| 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}, {10{{overline|1}}0}. {11{{overline|2}}0}

| cleavage = Perfect on {10{{overline|1}}1}

| 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 = n_ω = 1.690–1.750
n_ε = 1.510–1.548

| birefringence = δ = 0.180–0.202

| pleochroism =

| 2V =

| dispersion = Strong

| extinction =

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| references = [http://rruff.geo.arizona.edu/doclib/hom/ankerite.pdf Handbook of Mineralogy][http://www.mindat.org/min-239.html Ankerite on Mindat.org][http://webmineral.com/data/Ankerite.shtml Ankerite on Webmineral]

}}

Ankerite, also known as brown spar礦物學名詞: (俄英中对照試用本) Mineralogical Terminology (Russian-English-Chinese version). — Beijing: 中國科学院. 編譯出版委員会 Compilation and Publication Committee of Chinese Academy of Sciences, 1956. — 279 p.{{rp|258}} ({{langx|de|braunspat}}) is a calcium, iron, magnesium, manganese carbonate mineral of the group of rhombohedral carbonates with the chemical formula {{chem2|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. 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.

In 19th-century mineralogy, as well as in mining and among geologists, ankerite and its close analogues from the dolomite series were more often known by the capacious, expansive name of ″brown spar″.Bulletin of the United States National Museum. No.30. Published under the Directions of the Smithsonian Institution. — Washington: Government Printing Office, 1885.{{rp|34}} This is partly because this mineral is the extreme (with the highest content of divalent iron ions) member of the dolomite-ankerite isomorphic series, as a result of which dirty-brown varieties of dolomite, contaminated with impurities, could also be encountered under the name of brown spar.Krivovichev V. G. Mineralogical glossary. Scientific editor A. G. Bulakh. — St.Petersburg: St.Petersburg Univ. Publ. House. 2009. — 556 p. — ISBN 978-5-288-04863-0{{rp|70}}

Properties

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.{{EB1911|inline=y|wstitle=Ankerite|volume=2|page=58|first=Leonard James|last=Spencer|authorlink=Leonard James Spencer}}

Genesis

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 has been found in Western Tasmania, in mines in Dundas, Tasmania.