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Formula: FeNi
Alloy, iron-nickel group
Specific gravity: 8.28 calculated
Hardness: 3½
Streak: Grey
Colour: Grey-white, silver-white
Magnetism: Strongly magnetic
Common impurities: Co,Cu,P
Environments
Hydrothermal environments very rare
Meteorites
Tetrataenite is common in iron
meteorites, but very rare in terrestrial rocks
(Mindat).
In Meteorites
Tetrataenite occurs as exsolution rims and grains in slowly cooled
meteorites, by the ordering of
iron and nickel atoms in
taenite. It is most abundant in
mesosiderites and
chondrites. Associated minerals include
kamacite, troilite and
taenite
(AM 65.624-630, HOM).
In Terrestrial Rocks
Terrestrial tetrataenite has been found in an ophiolite-hosted
nickel-bearing magnetite body from the
Indo-Myanmar ranges, northeast India. Although the mineral assemblage surrounding it is very similar to that found in the
meteorites, the postulated cooling regimes cannot be similar.
Terrestrial tetrataenite is formed as a consequence of hydrothermal alteration of ferromagnesian minerals of the
olivine and pyroxene groups.
Iron and nickel were released from the silicates
and precipitated in the form of an iron-nickel
alloy at low temperature in extremely reducing conditions with a lack of sulphur. A
low temperature hydrothermal origin of tetrataenite is suggested
(AM 100.209-214). Associated minerals include chamosite,
magnetite, chromite and
chromium-aluminium
spinel
(HOM).
Localities
The type locality is the Estherville meteorite, Emmet county, Iowa, USA, where tetrataenite occurs as 10-50 micron
sized grains
(Mindat).
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