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Formula: SiC
Carbide
Crystal System: Hexagonal
Specific gravity: 3.218 to 3.220 measured
Hardness: 9½
Streak: Greenish grey
Colour: Green, black, blue, colourless, green-yellow, yellow
Environments
Igneous environments
Extraterrestrial environments
Naturally occurring moissanite is rare; it has been found as tiny crystals in some
iron meteorites (originally formed in star dust), as
inclusions in diamond, in
diamondiferous
kimberlite and
lamproite, in eclogite,
in volcanic breccia, in
rhyolite and in
alluvium. The synthetic form is a very important high-performance ceramic, more
commonly known as abrasive "carborundum"
(HOM, Mindat).
Localities
At the Fuxian kimberlite field, Wafangdian City, Dalian, Liaoning, China, moissanite occurs in a
diamond-bearing kimberlite pipe; its crystal
faces are coated by silicon and quartz is also present. Moissanite is inferred to have
formed during rapid ascent and consequent vesiculation of CO2-rich kimberlitic
magma at P-T conditions where high quartz is also stable, ie pressure less than 20-28 kbar but
greater than 10 kbar and temperature near
1000oC, and under more oxidising conditions than diamond
(AM 77.207-208).
An inclusion found in a diamond from Fuxian contains four blue-green moissanite crystals,
overgrown by apparently younger, colourless grains of a later generation. This multicrystalline cluster is surrounded by a thin layer of
potassium-aluminium-silicon rich glass
(AM 75.1110-1119 ).
In Bohemia, Czech Republic, a natural occurrence of moissanite is in
non-kimberlitic volcanic breccia in a
region of kimberlitic rocks. The moissanite is represented by a high-temperature
polymorph formed in the range from 1900 to 2000oC. This high temperature of formation and the presence of fragmental
crystals indicate that the moissanite and associated volcanic breccia came from a
great depth, but the moissanite is associated with distinctly hydrothermal minerals, such as
galena, pyrite and
fluorite, which normally form at shallower depths
(AM 48.620-634).
On a beach in the Aegean sea was found the first occurrence of moissanite as a rock-forming mineral (8.4 vol%) in one unique
specimen of a terrestrial rock. The sample has a homogeneous, porphyritic texture, and
was found as a beach pebble. The matrix consists of very fine-grained brucite,
calcite and magnesite, in which macrocrysts of
quartz and moissanite are found. Other accessory phases include
phlogopite, magnesiochromite,
chlorine-bearing brucite and aluminium-rich
orthopyroxene. The bulk-rock composition shows a
kimberlitic chemistry. The moissanite crystals are colourless, gemmy, and blue
or black. The indications are that the rock most likely formed at the ultrahigh-pressure conditions of the upper mantle or transition
zone
(AM 88.1817-1821).
At the Udachnaya open-pit mine, Daldyn, Mirninsky District, Sakha Republic, Russia, moissanite occurs in
kimberlite. Associated minerals include garnet,
coesite, clinopyroxene,
quartz, rutile,
graphite, pyrrhotite and
cobalt-bearing pyrite
(HOM).
The type locality is the Canyon Diablo meteorite, Meteor Crater area, Coconino County, Arizona, USA, where
moissanite is
reported to occur with iron and diamond
(HOM),
but according to (Dana) the
moissanite was probably a contaminant.
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