Augite (Clinopyroxene)  

Note the inclined extinction which is diagnostic of clinopyroxene. Also note the pigeonite twin lamellae in this grain. Pigeonite is a Ca-poor clinopyroxene.

Contrast clinopyroxene's inclined extinction with orthopyroxene's parallel extinction.

UNC sample

"norite" card

Rock type

clinopyroxenite

Locality

West Point, GA