Formula: Ni3Si2O5(OH)4
Phyllosilicate (sheet silicate), kaolinite-serpentine group, polymorph of népouite
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

Hydrothermal environments

Pecoraite occurs in shears in ultramafic rocks, and as a weathering product of millerite in geodes (Mindat).


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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