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The Mineral omphacite

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.
Chemical Formula (Ca,Na)(Mg,Fe2+,Fe3+,Al)Si2O6
Composition A silicate of calcium, sodium, magnesium, iron, and aluminum
Color Light to dark green
Streak White to light green
Hardness 5 - 6
Crystal System Monoclinic
Crystal Forms
and Aggregates
As prismatic or equant crystals with a square cross-section. Crystals are often twinned. Also grainy, massive, and encrusting.
Transparency Translucent to opaque. Rarely transparent.
Specific Gravity 3.3 - 3.4
Luster Vitreous, dull
Cleavage 1,2 - prismatic at cleavage angles of 87º and 93º (Characteristic of minerals in the pyroxene group).
Fracture Uneven
Tenacity Brittle
In Group Silicates; Inosilicates; Pyroxene Group
Striking Features Crystal forms, cleavage habits, and environment.
Environment A major constituent of eclogite deposits; also in other ultra-high pressure metamorphic rocks.
Rock Type Metamorphic
Popularity (1-4) 4
Prevalence (1-3) 3
Demand (1-3) 3

Omphacite AUCTIONS

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.

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

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

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