| Augite | |
|---|---|
 Augite –Muhavura volcano | |
| General | |
| Category | Inosilicates |
| Formula | (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6 |
| IMA symbol | Aug[1] |
| Strunz classification | 9.DA.15 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (sameH-M symbol) |
| Space group | C2/c |
| Unit cell | a = 9.699, b = 8.844 c = 5.272 [Å] β = 106.97°; Z = 4 |
| Identification | |
| Color | Black, brown, greenish, violet-brown; in thin section, colorless to gray with zoning common |
| Crystal 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 {110}; parting on {100} and {010} |
| Fracture | uneven to conchoidal |
| Tenacity | brittle |
| Mohs scale hardness | 5.5 to 6 |
| Luster | Vitreous, resinous to dull |
| Streak | Greenish-white |
| Diaphaneity | Transparent to opaque |
| Specific gravity | 3.19–3.56 |
| Optical properties | Biaxial (+) |
| Refractive index | nα = 1.680–1.735, nβ = 1.684–1.741, nγ = 1.706–1.774 |
| 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 |
| References | [2][3][4] |
Augite, also known asAugurite, is a common rock-formingpyroxenemineral with formula(Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6. Thecrystals aremonoclinic andprismatic. Augite has two prominent cleavages, meeting at angles near 90 degrees.
Augite is asolid solution in thepyroxene group.Diopside andhedenbergite are important endmembers in augite, but augite can also contain significantaluminium,titanium, andsodium and other elements. The calcium content of augite is limited by amiscibility gap between it andpigeonite andorthopyroxene: 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 andomphacite, but this gap occurs at higher temperatures. There are no industrial or economic uses for this mineral.[5][6]
Augite is an essential mineral inmaficigneous rocks; for example,gabbro andbasalt and common inultramafic rocks. It also occurs in relatively high-temperaturemetamorphic rocks such as maficgranulite and metamorphosed iron formations. It commonly occurs in association withorthoclase,sanidine,labradorite,olivine,leucite,amphiboles and other pyroxenes.[2]
Occasional specimens have a shiny appearance that give rise to the mineral's name, which is from the Greekaugites, meaning "brightness", although ordinary specimens have a dull (dark green, brown or black) luster. It was named byAbraham Gottlob Werner in 1792.[3]
