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Formula: Cu2+3(AsO4)(OH)3
Arsenate of copper, triclinic
paramorph of monoclinic
clinoclase
Crystal System: Triclinic
Specific gravity: 4.2 measured, 4.21 calculated for the empirical formula, 4.28 calculated for the ideal formula
Hardness: 3
Streak: Greenish blue
Colour: Greenish blue
Luminescence: Not fluorescent under UV
Solubility: Soluble in hydrochloric acid
Environments
Localities
At the type locality, the Roua Mines, Daluis, Nice Arrondissement, Alpes-Maritimes, Provence-Alpes-Côte d'Azur,
France, the cupriferous mineralisation is hosted in a gangue formed by
subvertical dolomite and calcite
veinlets, with accessory aragonite. The veinlets crosscut
pelites and red
sandstones and their thickness varies from a few mm to a few cm.
Gilmarite occurs in the Roua copper occurrences in two distinct zones
400 m apart, a northern and a southern zone lying, respectively, in the districts of Guillaume and Daluis.
The copper mineralisation at Roua consists of flake-shaped
native copper, sometimes several tens of cm in size with irregular contours,
and up to 3.5 cm thick, and small nodules. This copper occurs in the central
part of the veinlets, and is always associated with cuprite, copper
arsenides (domeykite,
algodonite, koutekite), and,
more rarely, native silver. Several rare
secondary mineral species have been recognised.
Gilmarite occurs in small geodes in association with cuprite,
posnjackite, langite,
tangdanite, connellite,
brochantite, malachite,
vesignieite, cornubite,
olivenite, trippkeite,
domeykite and djurleite.
Gilmarite forms rosettes of maximum size 0.3 mm across or isolated crystals of maximum size
0.1 × 0.04 x 0.02 mm3. The crystals are green-blue, transparent, with vitreous lustre and blue-green
streak
(EJM 11.3.549-556).
Gilmarite from the Roua Mines - Image
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