View source for Ankerite

{{Short description|Calcium, iron, magnesium, manganese carbonate mineral}}
{{Other uses|brown spar}}
{{Infobox mineral
| name        = Ankerite
| boxwidth    = 
| boxbgcolor  = 
| image       = Ankérite (Grandfontaine)-Musée de minéralogie de Strasbourg.jpg
| imagesize   = 260px
| alt         = 
| caption     = 
| category    = [[Carbonate mineral]]
| formula     = {{chem2|Ca(Fe,Mg,Mn)(CO3)2}}
|IMAsymbol=Ank<ref>{{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}}</ref>
| molweight   =  
| strunz      = 5.AB.10
| dana        = 
| system      = [[Trigonal]]
| class       = Rhombohedral ({{overline|3}}) <br/>[[H–M symbol]]: ({{overline|3}})
| symmetry    = ''R''{{overline|3}}
| unit cell   = ''a'' = 4.8312(2) <br/>''c'' = 16.1663(3)&nbsp;[Å]; ''Z''&nbsp;=&nbsp;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''<sub>ω</sub> = 1.690–1.750 <br> ''n''<sub>ε</sub> = 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  = <ref name=HBM>[http://rruff.geo.arizona.edu/doclib/hom/ankerite.pdf Handbook of Mineralogy]</ref><ref name=Mindat>[http://www.mindat.org/min-239.html Ankerite on Mindat.org]</ref><ref name=Webmin>[http://webmineral.com/data/Ankerite.shtml Ankerite on Webmineral]</ref>
}}
'''Ankerite''', also known as ''[[brown spar]]''<ref name="термин">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.</ref>{{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 (mineral)|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]].<ref name=Mindat/>

== Name and history ==
It was first recognized as a distinct species by [[Wilhelm Karl Ritter von Haidinger|Wilhelm von Haidinger]] in 1825, and named for [[Matthias Joseph Anker]] (1771–1843) of [[Styria]], an [[Austria]]n [[mineralogist]].<ref name=Mindat/>

In 19th-century mineralogy, as well as in mining and among geologists, ankerite and its close analogues from the [[Dolomite (mineral)|dolomite]] series were more often known by the capacious, expansive name of ″brown spar″.<ref name="muse">Bulletin of the United States National Museum. No.30. Published under the Directions of the Smithsonian Institution. — Washington: Government Printing Office, 1885.</ref>{{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]]''.<ref name="kriv">''Krivovichev V. G.'' Mineralogical glossary. Scientific editor [[:uk:Булах Андрій Глібович|A. G. Bulakh]]. — St.Petersburg: St.Petersburg Univ. Publ. House. 2009. — 556 p. — ISBN 978-5-288-04863-0</ref>{{rp|70}}

== Properties ==
The crystallographic and physical characters resemble those of [[Dolomite (mineral)|dolomite]] and [[siderite]]. The angle between the perfect rhombohedral cleavages is 73°&nbsp;48′, the [[Mohs hardness|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.<ref name="EB1911">{{EB1911|inline=y|wstitle=Ankerite|volume=2|page=58|first=Leonard James|last=Spencer|authorlink=Leonard James Spencer}}</ref>

== Genesis ==
Ankerite occurs with siderite in metamorphosed ironstones and sedimentary [[banded iron formation]]s. It also occurs in [[carbonatite]]s. In sediments it occurs as authigenic, [[Diagenesis|diagenetic]] minerals and as a product of [[hydrothermal]] deposition.<ref name=HBM/> 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.<ref name="EB1911"/>

It has been found in Western Tasmania, in mines in [[Dundas, Tasmania]].

== Image gallery ==
<gallery widths="165px" heights="130px">
File:Ankerite, Pyrite - Goldmyer Hot Springs, King Co, Washington, USA.jpg|Ankerite on pyrite from [[King County, Washington]]
File:Ankérite Quartz Pérou.jpg|Ankerite on [[quartz]] from Peru
</gallery>

==See also==
*[[List of minerals]]
*[[List of minerals named after people]]

==References==
{{Refbegin}}
{{Reflist}}
*[https://web.archive.org/web/20050404043159/http://mineral.galleries.com/minerals/carbonat/ankerite/ankerite.htm Mineral Galleries]
{{Refend}}

==External links==
{{commons category|Ankerite|position=left}}

{{Manganese minerals}}

[[Category:Calcium minerals]]
[[Category:Magnesium minerals]]
[[Category:Iron(II) minerals]]
[[Category:Manganese(II) minerals]]
[[Category:Carbonate minerals]]
[[Category:Dolomite group]]
[[Category:Trigonal minerals]]
[[Category:Minerals in space group 148]]
[[Category:Luminescent minerals]]