Augite
Augite, also known as Augurite, is a common rock-forming pyroxene mineral with formula (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.
| Augite | |
|---|---|
Augite – Muhavura volcano | |
| General | |
| Category | Inosilicates |
| Formula (repeating unit) | (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6 |
| IMA symbol | Aug |
| Strunz classification | 9.DA.15 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-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 | |
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