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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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