Augite
Image: Didier Descouens (CC BY-SA 4.0)
Mineral NameAugite
Chemical Formula(Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6
Mohs Hardness5.5
Crystal Systemmonoclinic
Lustervitreous
Streak Colorwhite to grayish-green
Cleavagegood in two directions at nearly 90 degrees (87 and 93 degrees)
Fractureuneven to conchoidal
Specific Gravity3.4
Colorsblack, dark green, brownish-black
Transparencyopaque
Type LocalityMuhavura volcano, Ruhengeri Region, Northern Province, Rwanda
Mineral GroupSilicates
Usesrock-forming mineral, collector
Associated Mineralsplagioclase feldspar, olivine, hornblende, magnetite
Raritycommon
Description
This specimen features dark, blocky augite crystals, ranging from subhedral to euhedral, embedded within a fine-grained, dark grey volcanic matrix. The crystals exhibit a subvitreous to dull luster and are well-defined against the lighter speckled groundmass.
Geological Context
Augite is a common rock-forming mineral found in mafic and intermediate igneous rocks, such as basalt and gabbro. Its occurrence at Muhavura volcano indicates its formation during the crystallization of magma in a volcanic environment.
