View source for Almandine

{{Short description|Species of mineral belonging to the garnet group}}
{{redirect|Almandin|the racehorse|Almandin (horse)}}
{{Distinguish|Amandine (disambiguation)}}
{{Infobox mineral
| name        = Almandine
| category    = [[Nesosilicate]]
| boxwidth    = 
| boxbgcolor  = #5C4342 
| boxtextcolor= white
| image       = Almandin.jpg
| imagesize   = 300px
| caption     = 
| formula     = {{chem|Fe|3|2+|Al|2|Si|3|O|12}}
|IMAsymbol=Alm<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      = 9.AD.25
| system      = [[Cubic crystal system|Cubic]]
| class       = Hexoctahedral (m{{overline|3}}m) <br/>[[H–M symbol]]: (4/m {{overline|3}} 2/m)
| symmetry    = ''I''a{{overline|3}}d
| color       = reddish orange to red, slightly purplish red to reddish purple and usually dark in tone 
| habit       = 
| twinning    = 
| cleavage    = none
| fracture    = conchoidal<ref name="GRG"/>
| mohs        = 7.0–7.5
| luster      = greasy to vitreous
| polish      = vitreous to subadamantine<ref name="GRG"/>
| refractive  = {{val|1.790|0.030}}<ref name="GRG">[[Gemological Institute of America]], ''GIA Gem Reference Guide'' 1995, {{ISBN|0-87311-019-6}}</ref>
| opticalprop = Single refractive, and often anomalous double refractive<ref name="GRG"/>
| birefringence = none
| dispersion  = 0.024<ref name="GRG"/>
| pleochroism = none
| fluorescence= inert
| absorption  = usually at 504, 520, and 573&nbsp;nm, may also have faint lines at 423, 460, 610 and 680–690&nbsp;nm<ref name="GRG"/>
| streak      = white
| gravity     = {{val|4.05|0.25|0.12}}<ref name="GRG"/>
| density     = 
| melt        = 
| fusibility  = 
| diagnostic  = 
| solubility  = 
| diaphaneity = 
| other       = 
| references  = <ref>[http://www.mindat.org/min-452.html Mindat.org - Almandine]</ref><ref>[http://www.webmineral.com/data/Almandine.shtml Webmineral.com - Almandine]</ref><ref>{{Cite web |url=http://www.handbookofmineralogy.com/pdfs/almandine.pdf |title=Handbook of Mineralogy - Almandine |access-date=2013-03-01 |archive-date=2016-03-03 |archive-url=https://web.archive.org/web/20160303170453/http://www.handbookofmineralogy.com/pdfs/almandine.pdf |url-status=dead }}</ref>
}}

'''Almandine''' ({{IPAc-en|ˈ|æ|l|m|ən|d|ɪ|n}}), also known as '''almandite''', is a mineral belonging to the [[garnet]] group. The name is a corruption of alabandicus, which is the name applied by [[Pliny the Elder]] to a stone found or worked at [[Alabanda]], a town in [[Caria]] in [[Asia Minor]]. Almandine is an iron aluminium garnet, of deep red color, inclining to purple. It is frequently cut with a convex face, or en [[cabochon]], and is then known as [[Carbuncle (gemstone)|carbuncle]]. Viewed through the [[spectroscope]] in a strong light, it generally shows three characteristic [[absorption band]]s.<ref name="EB1911">{{EB1911|inline=y|wstitle=Almandine|volume=1|page=712}}</ref>

Almandine is one [[Endmember (mineralogy)|end-member]] of a mineral [[solid solution]] series, with the other end member being the garnet [[pyrope]]. The almandine crystal formula is: Fe<sub>3</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub>. [[Magnesium]] substitutes for the [[iron]] with increasingly pyrope-rich composition.

Almandine, {{chem|Fe|3|2+|Al|2|Si|3|O|12}}, is the [[Iron(II)|ferrous iron]] end member of the class of garnet minerals representing an important group of rock-forming [[Silicate mineral|silicates]], which are the main constituents of the Earth's [[crust (geology)|crust]], [[upper mantle]] and [[Transition zone (Earth)|transition zone]]. Almandine crystallizes in the cubic [[space group]] ''I''a{{overline|3}}d, with unit-cell parameter ''a''&nbsp;≈&nbsp;11.512&nbsp;Å at 100&nbsp;K.<ref name="Paper 1">{{cite journal|last1=Geiger |first1=C. |last2=Armbruster |first2=Th. |last3=Lager |first3=G. |last4=Jiang |first4=K. |last5=Lottermoser |first5=W. |last6=Amthauer |first6=G. |date=1992 |title=A combined temperature dependent <sup>57</sup>Fe Mössbauer and single crystal X-ray diffraction study of synthetic almandine: evidence for the Gol'danskii–Karyagin effect. |journal=Physics and Chemistry of Minerals |volume=19 |issue=2 |pages=121–126 |doi=10.1007/BF00198609|bibcode=1992PCM....19..121G |s2cid=98610041 }}</ref>

Almandine is [[antiferromagnet]]ic with the [[Néel temperature]] of 7.5&nbsp;K. It contains two equivalent magnetic sublattices.<ref name="Thesis">{{cite thesis|first=Danylo |last=Zherebetskyy |date=2010 |title=Quantum mechanical first principles calculations of the electronic and magnetic structure of Fe-bearing rock-forming silicates |type=PhD |publisher=Dissertation.com, Boca Raton, Florida |isbn=978-1-59942-316-6 |url=http://www.universal-publishers.com/book.php?method=ISBN&book=1599423162}}</ref>

==Occurrence==
[[File:Victorian almandine garnet brooch.jpg|thumb|left|A 19th-century almandine garnet brooch]]
Almandine occurs rather abundantly in the gem gravels of [[Sri Lanka]], whence it has sometimes been called "Ceylon ruby". When the color inclines to a violet tint, the stone is often called Syriam garnet, a name said to be taken from [[Thanlyin|Syriam]], an ancient town of [[Bago, Burma|Pegu]] (now part of [[Burma|Myanmar]]). Large deposits of fine almandine-garnets were found, some years ago, in the [[Northern Territory]] of [[Australia]], and were at first taken for rubies and thus they were known in trade for some time afterwards as Australian rubies.

Almandine is widely distributed. Fine [[Rhombic dodecahedron|rhombic dodecahedra]] occur in the [[schist]]ose rocks of the [[Zillertal]], in [[Tyrol]], and are sometimes cut and polished. An almandine in which the ferrous oxide is replaced partly by [[Magnesium oxide|magnesia]] is found at a place once known as Luisenfeld (then [[German East Africa]]), now in [[Tanzania]]. In the [[United States]] there are many localities which yield almandine. Fine crystals of almandine embedded in [[mica]]-schist occur near [[Wrangell, Alaska|Wrangell]] in [[Alaska]]. The coarse varieties of almandine are often crushed for use as an [[abrasive]] agent.

==Cultural significance==
[[Connecticut]] has designated almandine garnet as its state gemstone.<ref>{{cite web |url=http://www.ct.gov/ctportal/cwp/view.asp?a=885&q=246586 |archive-url=https://web.archive.org/web/20020724110309/http://www.ct.gov/ctportal/cwp/view.asp?a=885&q=246586 |url-status=dead |archive-date=July 24, 2002 |title=State of Connecticut – Sites, Seals and Symbols |access-date=2009-11-12 |publisher=State of Connecticut}}</ref>

==See also==
{{commons category}}
{{Wiktionary}}
* [[List of minerals]]

==References==
{{Reflist}}

{{Gemstone}}

[[Category:Garnet gemstones]]
[[Category:Cubic minerals]]
[[Category:Minerals in space group 230]]