# Augite

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{{Short description|Common rock-forming pyroxene mineral}}
{{Infobox mineral
| name        = Augite
| category = [Inosilicate](/source/Inosilicate) minerals (single chain)
| group = [Pyroxene](/source/Pyroxene) group, clinopyroxene subgroup
| image       = Augite Rwanda.jpg
| imagesize   = 260px
| alt         = 
| caption     = Augite – [Muhavura volcano](/source/Mount_Muhabura)
| 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](/source/Monoclinic)
| class       = Prismatic (2/m) <br /><small>(same [H-M symbol](/source/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](/source/pyroxene) [mineral](/source/mineral) with formula {{chem2|(Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6}}. The [crystal](/source/crystal)s are [monoclinic](/source/monoclinic) and [prismatic](/source/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](/source/Teide) (4.4 x 3.0 x 2.3 cm)]]
Augite is a [solid solution](/source/solid_solution) in the [pyroxene](/source/pyroxene) group. [Diopside](/source/Diopside) and [hedenbergite](/source/hedenbergite) are important endmembers in augite, but augite can also contain significant [aluminium](/source/aluminium), [titanium](/source/titanium), and [sodium](/source/sodium) and other elements. The calcium content of augite is limited by a [miscibility gap](/source/miscibility_gap) between it and [pigeonite](/source/pigeonite) and [orthopyroxene](/source/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](/source/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](/source/mafic) [igneous rock](/source/igneous_rock)s; for example, [gabbro](/source/gabbro) and [basalt](/source/basalt) and common in [ultramafic](/source/ultramafic) rocks. It also occurs in relatively high-temperature [metamorphic rock](/source/metamorphic_rock)s such as mafic [granulite](/source/granulite) and metamorphosed iron formations. It commonly occurs in association with [orthoclase](/source/orthoclase), [sanidine](/source/sanidine), [labradorite](/source/labradorite), [olivine](/source/olivine), [leucite](/source/leucite), [amphibole](/source/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](/source/Abraham_Gottlob_Werner) in 1792.<ref name=Mindat/>

==See also==
* [Fassaite](/source/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](/source/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:Monoclinic minerals
Category:Minerals in space group 15
Category:Gemstones
Category:Minerals described in 1792
Category:Clinopyroxene subgroup

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Adapted from the Wikipedia article [Augite](https://en.wikipedia.org/wiki/Augite) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Augite?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.