View source for Eucryptite

{{Infobox mineral
| name        = Eucryptite
| category    = [[Silicate mineral]]
| image       = Eucryptite-202043.jpg
| imagesize   =
| caption     = Eucryptite grains in albite from the type locality (size: 9.3 × 7.0 × 2.8 cm)
| formula     = LiAlSiO<sub>4</sub>
| IMAsymbol   = Ecp<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>
| system      = [[Trigonal crystal system|Trigonal]]
| class       = Rhombohedral ({{overline|3}}) <br/>[[H-M symbol]]: ({{overline|3}})
| symmetry    = ''R''{{overline|3}}
| unit cell   = a = 13.48, c = 9.01&nbsp;[Å]; Z&nbsp;=&nbsp;18
| color       = Brown, colorless, white
| habit       = Rare as euhedral crystals, coarse crystalline aggregates and massive
| cleavage    = Indistinct on {10{{overline|1}}0} and {0001}
| fracture    = Conchoidal
| tenacity    = Very brittle
| mohs        = 6.5
| luster      = Vitreous
| refractive  = n<sub>ω</sub> = 1.570 – 1.573 n<sub>ε</sub> = 1.583 – 1.587
| opticalprop = Uniaxial (+)
| birefringence = δ = 0.013
| streak      = White
| density     = 2.67
| diaphaneity = Transparent to translucent
| other       = Fluoresces pink to red or orange under SW UV
| references  = <ref name=Mindat>[http://www.mindat.org/min-1364.html Mindat.org]</ref><ref name=Handbook>[http://rruff.geo.arizona.edu/doclib/hom/eucryptite.pdf Handbook of Mineralogy]</ref><ref>[http://webmineral.com/data/Eucryptite.shtml Webmineral data]</ref>
}}

'''Eucryptite''' is a [[lithium]] bearing aluminium [[silicate minerals|silicate mineral]] with formula LiAlSiO<sub>4</sub>. It crystallizes in the [[Trigonal crystal system|trigonal – rhombohedral]] [[crystal system]]. It typically occurs as granular to massive in form and may [[pseudomorph]]ically replace [[spodumene]]. It has a brittle to conchoidal fracture and indistinct cleavage. It is transparent to translucent and varies from colorless to white to brown. It has a Mohs hardness of 6.5 and a specific gravity of 2.67. Optically it is uniaxial positive with [[refractive index]] values of nω = 1.570 – 1.573 and nε = 1.583 – 1.587.

Its typical occurrence is in lithium-rich [[pegmatite]]s in association with [[albite]], [[spodumene]], [[petalite]], [[amblygonite]], [[lepidolite]] and [[quartz]].<ref name=Handbook/>

It occurs as a secondary alteration product of [[spodumene]]. It was first described in 1880 for an occurrence at its [[Type locality (geology)|type locality]], [[Branchville, Connecticut]].<ref name=Mindat/> Its name was from the [[Greek language|Greek]] for ''well concealed'', for its typical occurrence embedded in albite.<ref name=Mindat/><ref name=Handbook/>

==References==
{{Reflist}}
{{Lithium compounds}}
[[Category:Nesosilicates]]
[[Category:Lithium minerals]]
[[Category:Trigonal minerals]]
[[Category:Minerals in space group 148]]


{{Silicate-mineral-stub}}