SILICATES; INOSILICATES; PYROXENE GROUP · MONOCLINIC

Omphacite

About

Omphacite is a rare member of the pyroxene group. It is intermediary in chemical composition between Augite and Jadeite. It is one of the primary minerals that forms eclogite deposits, which is a dense, course grained rock formed at extremely high pressures. It is occasionally associated with Diamond in Diamond deposits.

Crystal Forms & Aggregates

As prismatic or equant crystals with a square cross-section. Crystals are often twinned. Also grainy, massive, and encrusting.

Striking Features

Crystal forms, cleavage habits, and environment.

Environment

A major constituent of eclogite deposits; also in other ultra-high pressure metamorphic rocks.

Noteworthy Localities

First described in Stammbach, Bavaria, Germany. Also found in Found in Val d'Osta (Ivrea), and Bric Vert, Italy; Hof, Bayreuth, Germany; Andersdorf, Koralpe Mountains, Austria; Sogn og Fjordane, Norway; and Oyashirazu beach, Itoigawa, Japan. In the U.S, it is found at Reeds Station in the Tiburon Peninsula, Marin County, California; and in Healdsburg, Sonoma Co., California.

Common Mineral Associations

Quartz, Biotite, Muscovite, Glaucophane, Almandine, Pyrope, Kyanite, Coesite

Distinguishing Similar Minerals

May be difficult to distinguish from other pyroxene minerals such as Augite, Enstatite, and Hedenbergite.

Abouti

Crystal Forms & Aggregatesi

Striking Featuresi

Environmenti

Noteworthy Localitiesi

Common Mineral Associationsi

Distinguishing Similar Mineralsi