The mineral pyroxene is a name applied to a group of silicates that are similar in composition to the hornblende group, but not so often containing soda and potash. Cleavage pieces show angles of 93° and 87°, thus making nearly square edges, a clear distinction between them and the sharp and obtuse edges of cleavage pieces of hornblende.

Augite

Augite, common pyroxene, is usually dull green, grayish, brown, black, sometimes white, rarely bright green or blue; powder white, gray or grayish-green; luster, glassy or dull; H = 5 to 6; G = 3.2 to 3.6; crystals, in monoclinic system; cleavage, sometimes rather perfect; composition, silicate of magnesia, lime, alumina, and iron. Augite is a characteristic mineral of basic igneous rocks, such as gabbro and diabase.

Diopside

Diopside contains little or no alumina; color, white, light green, or gray. Is found in crystalline limestone, especially in igneous contact zones. It is the common pyroxene of the mica deposits in Ontario and Quebec.

Diallage

Diallage is a pyroxene of green or brown color and lamellar (thin platy) structure; the characteristic pyroxene of gabbro, etc.; perhaps only a variety of augite.

Hypersthene

Hypersthene is a pyroxene of dark, brownish green, grayish black, or brown color; powder, grayish or brownish gray; luster, somewhat pearly, or slightly metallic on a cleavage surface; is high in iron, up to about 25%. Is a common constituent of such dark basic rocks as norite, gabbro, etc.

Enstatite

Enstatite is a pyroxene of white, grayish green, olive-green, or brown color; found characteristically in peridotites and serpentines derived from them; composition, MgSiO3, sometimes with iron.

Jadeite

Jadeite is a hard, very tough mineral of various shades of green; H = 6.5 to 7. It is related to pyroxene in properties, but is somewhat different in composition, being a silicate of soda and alumina. This mineral and similar varieties of hornblende and the like, have long been used by man in the manufacture of jade ornaments and implements, the finer varieties being still in use for ornaments.

Spodumene

Spodumene LiAlSi2O6, is gray, green, yellow, purple; powder, white; H = 6.5 to 7; G = 3.13 to 3.20; crystals, monoclinic; cleavage, good. The green variety, hiddenite, is used as a gem. Spodumene is valuable as raw material for making lithium medicines and other lithium chemicals, and during recent years has been much in demand in connection with nuclear development. With it are often found two other lithium minerals, lepidolite and amblygonite. Found in pegmatite granite and in gneiss.