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Formula: Ni3Si2O5(OH)4
Phyllosilicate (sheet silicate), serpentine subgroup,
polymorph of népouite,
nickel-bearing mineral
Crystal System: Monoclinic
Specific gravity: 3.084 measured, 3.47 calculated
Hardness: 2½
Streak: Light green
Colour: Green, blue-green yellow-green
Common impurities: Al,Fe,Mg,Ca,H2O
Environments
Hydrothermal environments
Meteorites
Pecoraite occurs in shears in ultramafic rocks, and as a weathering
product of millerite in geodes
(Mindat).
Localities
At the Otway Ni deposit, Nullagine, East Pilbara Shire, Western Australia, pecoraite is found along shears in
ultramafic rocks, associated with
millerite, gaspéite,
otwayite and nullaginite
(HOM).
At the type locality, the Wolfe Creek meteorite crater, Carranya Station, Halls Creek Shire, Western Australia,
pecoraite occurs as green grains, 0.1 to 5 mm in size, filling cracks in fragments of the weathered
nickel-iron meteorite. It is associated with
maghemite, quartz,
goethite, cassidyite and
reevesite
(AM 54.1740-1741, HOM).
At the Clear Creek claim, Goat Mountain, New Idria Mining District, San Benito county, California, USA, light apple-green spheroidal
masses and minute spear-shaped crystals of pecoraite occur sparingly, usually attached to
quartz or cinnabar. The
pecoraite is generally associated with native mercury,
edgarbaileyite and szymanskiite, and
apparently formed by alteration of nickel-bearing sulphides
(millerite and donharrisite) with which it
is closely associated
(Minrec 36.4.355).
In the St. Louis and Spergen limestones, St. Louis county, Missouri, USA, pecoraite occurs in geodes with
millerite
(HOM).
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