Augite
The common dark high-calcium pyroxene of basalts, from Earth to the Moon, Mars and Vesta.
Key facts
- Formula
- (Ca,Mg,Fe)2Si2O6
- Family
- Silicates
- Crystal system
- Monoclinic
What it is
Augite is a pyroxene with calcium making up about a quarter to nearly half of its metal sites, together with magnesium and iron, and often some aluminium, titanium and sodium. It is the most widespread pyroxene in volcanic rocks on Earth.
Where it is found
It is the main mineral of the nakhlites, Martian rocks made largely of augite crystals that settled in a lava flow or shallow intrusion about 1.3 billion years ago. It also occurs in shergottites, eucrites, angrites, lunar basalts, and as a minor mineral in ordinary chondrites, where it grows during heating.
How it is recognised
Augite is dark green to black, with stubby crystals and two cleavages at about 87° and 93°. In thin section it is pale brown or green with bright interference colours and an extinction angle of about 40°.
Did you know?
Nakhla, the meteorite that fell in Egypt in 1911, is about three-quarters augite.
Augite is named from the Greek for brightness, after the sheen of its cleavage faces.