Grimaldiite

grimaldiite

bracewellite

guyanaite

mcconnellite

Images

Formula: CrO(OH)
Oxide-hydroxide of chromium, trigonal paramorph of orthorhombic bracewellite and orthorhombic guyanaite
Crystal System: Trigonal
Specific gravity: 4.11 to 4.12 measured, 4.13 calculated
Hardness: 3½ to 4½
Streak: Red
Colour: Deep red to pinkish brown
Environments

Sedimentary environments
Hydrothermal environments

Localities

At the Virgen de Surumi mine, Pakajake Canyon, Colquechaca, Colquechaca Municipality, Chayanta Province, Potosí, Bolivia, a small specimen, 5 x 3 x 2 cm3, of penroseite and baryte has been found in a hydrothermal mineral deposit. The penroseite contains small cracks and cavities, partially coated with pinkish brown grimaldiite forming radially bladed aggregates of small (0.25 mm) partial spheres or scallop-shaped platy aggregates up to 5 mm across. The grimaldiite contains minute inclusions of an unidentified lead selenide and a mercury selenide (MM 48.560-562, HOM [locality erroneously given as the nearby Hiaca mine]).

At the type locality, the Merume River, Rest of Region 8, Potaro-Siparuni Region, Guyana, grimaldiite occurs in fine-grained intergrowth with other chromium oxide-hydroxide minerals in alluvial gravels, Associated minerals include bracewellite, eskolaite, guyanaite and mcconnellite (HOM).
Grimaldiite from the Merume River - Image

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