View source for Augite

{{Short description|Common rock-forming pyroxene mineral}}
{{Infobox mineral
| name        = Augite
| category    = [[Inosilicates]]
| image       = Augite Rwanda.jpg
| imagesize   = 260px
| alt         = 
| caption     = Augite – [[Mount Muhabura|Muhavura volcano]]
| formula     = {{chem2|(Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6}}
|IMAsymbol=Aug<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.DA.15
| system      = [[Monoclinic]]
| class       = Prismatic (2/m) <br /><small>(same [[H-M symbol]])</small>
| symmetry    = ''C2/c''
| unit cell   = a = 9.699, b = 8.844 <br />c = 5.272&nbsp;[Å] <br />β = 106.97°; Z&nbsp;=&nbsp;4
| color       = Black, brown, greenish, violet-brown; in thin section, colorless to gray with zoning common
| habit       = Commonly as stubby prismatic crystals, also acicular, skeletal, dendritic
| twinning    = Simple or multiple on {100} and {001}
| cleavage    = {110} good with 87° between {110} and {1{{overline|1}}0}; parting on {100} and {010}
| fracture    = uneven to conchoidal
| tenacity    = brittle
| mohs        = 5.5 to 6
| luster      = Vitreous, resinous to dull
| refractive  = n<sub>α</sub> = 1.680–1.735, n<sub>β</sub> = 1.684–1.741, n<sub>γ</sub> = 1.706–1.774
| opticalprop = Biaxial (+)
| birefringence = δ = 0.026–0.039
| pleochroism = X = pale green, pale brown, green, greenish yellow; Y = pale brown, pale yellow-green, violet; Z = pale green, grayish green, violet
| streak      = Greenish-white
| gravity     = 3.19–3.56
| density     =
| melt        =
| fusibility  =
| diagnostic  =
| solubility  =
| diaphaneity = Transparent to opaque
| other       =
| references  = <ref name=HBM>[http://rruff.geo.arizona.edu/doclib/hom/augite.pdf Handbook of Mineralogy]</ref><ref name=Mindat>[http://www.mindat.org/min-419.html Augite on Mindat.org]</ref><ref name=Webmin>[http://webmineral.com/data/Augite.shtml Webmineral data for Augite]</ref>
}}

'''Augite''', also known as '''Augurite''', is a common rock-forming  [[pyroxene]] [[mineral]] with formula {{chem2|(Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6}}. The [[crystal]]s are [[monoclinic]] and [[prismatic]]. Augite has two prominent cleavages, meeting at angles near 90 degrees.

==Characteristics==
[[File:Augite-54563.jpg|thumb|upright|left|Euhedral crystal of augite from [[Teide]] (4.4 x 3.0 x 2.3 cm)]]
Augite is a [[solid solution]] in the [[pyroxene]] group. [[Diopside]] and [[hedenbergite]] are important endmembers in augite, but augite can also contain significant [[aluminium]], [[titanium]], and [[sodium]] and other elements. The calcium content of augite is limited by a [[miscibility gap]] between it and [[pigeonite]] and [[orthopyroxene]]: when occurring with either of these other pyroxenes, the calcium content of augite is a function of temperature and pressure, but mostly of temperature, and so can be useful in reconstructing temperature histories of rocks. With declining temperature, augite may exsolve lamellae of pigeonite and/or orthopyroxene. There is also a miscibility gap between augite and [[omphacite]], but this gap occurs at higher temperatures. There are no industrial or economic uses for this mineral.<ref name="kleiin-hurlbut-1993">{{cite book |last1=Klein |first1=Cornelius |last2=Hurlbut |first2=Cornelius S. Jr. |title=Manual of mineralogy : (after James D. Dana) |date=1993 |publisher=Wiley |location=New York |isbn=047157452X |edition=21st |pages=481–482}}</ref><ref name="nesse-2000">{{cite book |last1=Nesse |first1=William D. |title=Introduction to mineralogy |date=2000 |publisher=Oxford University Press |location=New York |isbn=9780195106916 |pages=268–269}}</ref>

==Locations==
Augite is an essential mineral in [[mafic]] [[igneous rock]]s; for example, [[gabbro]] and [[basalt]] and common in [[ultramafic]] rocks. It also occurs in relatively high-temperature [[metamorphic rock]]s such as mafic [[granulite]] and metamorphosed iron formations. It commonly occurs in association with [[orthoclase]], [[sanidine]], [[labradorite]], [[olivine]], [[leucite]], [[amphibole]]s and other pyroxenes.<ref name=HBM/>

Occasional specimens have a shiny appearance that give rise to the mineral's name, which is from the Greek ''augites'', meaning "brightness", although ordinary specimens have a dull (dark green, brown or black) luster. It was named by [[Abraham Gottlob Werner]] in 1792.<ref name=Mindat/>

==See also==
* [[Fassaite]]

==References==
{{Reflist}}

==Further reading==
{{Commons category|Augite}}
* Deer, W. A., Howie, R. A., and Zussman, J. (1992). ''[[An introduction to the rock-forming minerals]] (2nd ed.)''. Harlow: Longman {{ISBN|0-582-30094-0}}

{{Authority control}}

[[Category:Sodium minerals]]
[[Category:Calcium minerals]]
[[Category:Magnesium minerals]]
[[Category:Iron minerals]]
[[Category:Pyroxene group]]
[[Category:Monoclinic minerals]]
[[Category:Minerals in space group 15]]
[[Category:Gemstones]]
[[Category:Minerals described in 1792]]