Staff member
Jun 3, 2020
Augite is a common rock-forming pyroxene mineral that commonly occurs in mafic and intermediate igneous rocks such as basalt, andesite, gabbro, and diorite. It is also found in ultramafic rocks and in some metamorphic rocks that form under high temperatures.

Augite is usually green, black, or brown in color with formula (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6. It exhibits two prominent cleavage directions that intersect at angles slightly less than 90 degrees. The cleavage is difficult to observe, particularly in fine-grained rocks. So, a hand lens is often required. The crystals are monoclinic and prismatic. The luster is either vitreous (crystal faces) or dull (other surfaces). Augite has a Mohs hardness of 5.5 to 6, and specific gravity of 3.2 to 3.6.

It has no commercial use but the calcium content has limited use in studying the temperature history of rocks. Augite is also found in lunar basalts and meteorites.

Physical Properties

Crystal SystemMonoclinic
ColorGreen, black, brown
LusterVitreous, resinous to dull
CleavagePrismatic in 2 directions that intersect at 90 degrees
Mohs Scale Hardness5.5 to 6
DiaphaneityTransparent to opaque
Specific Gravity3.2 to 3.6
Chemical Composition(Ca,Na)(Mg,Fe,Al)(Si,Al)2O6
Diagnostic PropertiesColor, specific gravity, and cleavage.


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