Diallage

Diallage, a variety of augite, crystallising in the oblique system, with more perfect cleavage than augite (q.v.), the same absence of pleochroism, and a pearly or sub-metallic lustre. Its crystals often contain numerous acicular microliths arranged in definite directions, and fluid-cavities. By ordinary transmitted light they are pale green or brownish yellow. With labradorite felspar this mineral makes up the rockgabbro (q.v.). Its hardness is 4 and its specific gravity about 3.20.