{{Short description|Sulfosalt mineral}} {{Infobox mineral | name = Alloclasite | boxwidth = | boxbgcolor = | image = | imagesize = | alt = | caption = | struct image = | struct caption = | struct imagesize = | struct2 image = | struct2 caption = | struct2 imagesize= | SMILES = | Jmol = | category = | formula = {{chem2|(Co,Fe)AsS}} | IMAsymbol = All | molweight = | strunz = | dana = | system = | class = | symmetry = | unit cell = | color = Steel gray to silver | colour = | habit = | twinning = | cleavage = | fracture = Irregular/Uneven, Sub-Conchoidal | tenacity = | toughness = | mohs = 5 | luster = Metallic | streak = Nearly black | diaphaneity = Opaque | gravity = 5.95 | density = | polish = | opticalprop = | refractive = | birefringence = | pleochroism = | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | Curie temp = | fusibility = | diagnostic = | solubility = | impurities = | alteration = | other = | prop1 = | prop1text = | references = | var1 = | var1text = | var2 = | var2text = | var3 = | var3text = | var4 = | var4text = | var5 = | var5text = | var6 = | var6text = }} '''Alloclasite''', or {{chem2|(Co,Fe)AsS}}, is a sulfosalt mineral (IMA symbol: Acl).<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> It is a member of the arsenopyrite group. Alloclasite crystallizes in the monoclinic system and typically forms as columnar to radiating acicular prismatic clusters. It is an opaque steel-gray to silver-white, with a metallic luster and a black streak. It is brittle with perfect cleavage, a Mohs hardness of 5 and a specific gravity of 5.91–5.95.<ref name=Handbook>http://rruff.geo.arizona.edu/doclib/hom/alloclasite.pdf Handbook of Mineralogy</ref>
It was first described in 1866 for an occurrence in Romania.<ref>http://www.mindat.org/min-134.html Mindat data</ref> Its name is derived from Greek for "other" and "to break," in reference to its distinct cleavage which distinguished it from the similar appearing mineral marcasite.<ref>http://www.webmineral.com/data/Alloclasite.shtml Webmineral data</ref><ref name=Handbook/>
The mineral is monoclinic in the ''P2<sub>1</sub>'' space group.<ref>{{cite journal |last1=Scott |first1=J.D. |last2=Nowacki |first2=W. |journal=The Canadian Mineralogist |volume=14 |year=1976 |pages=561–566 |title=The crystal structure of alloclasite, CoAsS, and the alloclasite-cobaltite transformation}}</ref>
== References == {{Reflist}}
Category:Cobalt minerals Category:Iron minerals Category:Sulfosalt minerals Category:Monoclinic minerals Category:Minerals in space group 4 Category:Minerals described in 1866
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