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Formula: Fe2+V3+2O4
Oxide, spinel subgroup,
oxyspinel group,
spinel supergroup,
vanadium-bearing mineral
Crystal System: Isometric
Specific gravity: 5.17 to 5.20 measured, 5.15 calculated
Hardness: 4½ to 5
Streak: Black-brown
Colour: Bluish grey
Environments
Localities
At Panzhihua, Sichuan, China, coulsonite has been found exsolved from
magnetite in a mantle xenolith in
basalt
(HOM).
At the type locality, the Buena Vista Iron Mine, Mineral Basin Mining District, Churchill County, Nevada, USA,
coulsonite was found closely associated with magnetite and
chlorine-rich scapolite in the metamorphosed igneous rocks. The host rock
is hornblende andesite
and the evenly distributed fine-grained
magnetite probably represents a
primary constituent in the rock. Veinlets of
magnetite, in association with chlorine-rich
scapolite, apatite,
titanite, and alkali pyroxenes and
amphiboles cut the andesite.
Coulsonite is found only with these late magnetite veinlets. It
occurs along the octahedral planes in magnetite, and less commonly as
subhedral crystals isolated in a matrix of scapolite,
chlorite, hornblende and
muscovite. The first type may have been formed by exsolution of
vanadium from magnetite followed
by limited replacement of magnetite by coulsonite localised at
octahedral plane intersections
(AM 47.1284-1291).
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