Augite

Augite
General
Category	Mineral
Chemical formula	(Ca, Mg, Fe, Ti, Al)(Al, Si)2O6
Identification
Colour	Pale brown to purplish or greenish brown
Crystal system	Monoclinic
Cleavage	{110} good
Fracture	uneven
Mohs Scale hardness	5 to 6.5
Luster	Vitreous
Refractive index	α = 1.671 - 1.735, β = 1.672 - 1.741, γ = 1.703 - 1.774
Specific gravity	3.19 - 3.56
Data from Deer et al. (1992).

Augite is a mafic mineral described chemically as (Ca, Na)(Mg, Fe, Al)(Al, Si)₂O₆ or calcium sodium magnesium iron aluminium silicate. Structurally, it is a solid solution of the pyroxene group which also contains diopside and hedenbergite. The crystals are monoclinic and prismatic. It is found in igneous rocks such as gabbros and basalts, and in metamorphic rocks from hydrothermal vents. 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) finish.

References

• 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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