{{Short description|Common rock-forming pyroxene mineral}} {{Infobox mineral | name = Augite | category = Inosilicate minerals (single chain) | group = Pyroxene group, clinopyroxene subgroup | image = Augite Rwanda.jpg | imagesize = 260px | alt = | caption = Augite – 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 crystals 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 rocks; for example, gabbro and basalt and common in ultramafic rocks. It also occurs in relatively high-temperature metamorphic rocks such as mafic granulite and metamorphosed iron formations. It commonly occurs in association with orthoclase, sanidine, labradorite, olivine, leucite, amphiboles 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}}

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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