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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




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.


 
ADDITIONAL RESOURCES
 
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