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Formula: CuMg[Te6+O4(OH)2].6H2O
Hydrated tellurate
Crystal System: Monoclinic
Specific gravity: 2.82 measured, 2.828 calculated for the empirical formula
Hardness: 2
Streak: White
Colour: Light blue to bright sky-blue
Environments
Raisaite is a relatively new mineral, approved in 2014.
Localities
The type locality, the Sentyabr’skoe deposit, Ilirney ore district, Chaunskii District, Chukotka Autonomous
Okrug, Russia, is a silver and gold
deposit, located within Early Cretaceous (145 to 100.5 million years ago) volcanic rocks, mainly
andesite, basaltic
andesite, dacite,
rhyolite and their tuffs.
These rocks are intruded by Late Cretaceous (100.5 to 66 million years ago)
quartz monzonite,
granodiorite and
granitic porphyry.
The deposit consists of numerous hydrothermal veins, from 5 to 30 cm thick, surrounded by aureoles of
propylite and
quartz–sericite and
quartz–kaolinite rocks. Ores of
the deposit were formed at 350 to
280oC and pressure of 250 to 380 bars.
Raisaite is a secondary,
supergene mineral found in minor amounts in the oxidation
zone comprising quartz veins with carbonates
(calcite, dolomite and
ankerite), muscovite,
nacrite and chamosite and
containing a rich ore mineralisation represented by pyrite,
chalcopyrite, galena,
sphalerite, acanthite,
gold, hessite,
petzite, altaite and
coloradoite. The
supergene minerals occur in cracks and small cavities within
slightly oxidised near-surface parts of ore veins. These include gypsum,
malachite, azurite,
cerussite, anglesite,
brochantite, linarite,
posnjakite,
secondary gold and
acanthite, chlorargyrite,
brucite, goethite,
coronadite, paratellurite,
xocomecatlite and raisaite.
Carbonates of the
dolomite–ankerite series are an
obvious source of Mg, chalcopyrite of Cu, and
tellurides, hessite,
petzite and altaite, of Te for
raisaite formation.
Raisaite occurs as prismatic crystals which form radial, bush-like or chaotic groups and crystal crusts.
Separate crystals are typically up to 0.15 mm long and 0.03 mm thick, very rarely up to 0.6 mm long and 0.1 mm
thick. Crystal crusts are up to 0.4 x 0.6 mm2 in size. Raisaite overgrows
dolomite, quartz,
muscovite, chalcopyrite,
hessite and petzite. In some
cracks, colourless, transparent, coarse-crystalline gypsum crusts cover
aggregates of the raisaite.
Raisaite is transparent, light blue to bright sky blue, with a white streak and vitreous lustre
(EJM 28.2.459-466).
Raisaite from Sentyabr’skoe - Image
At the Upper dumps, North Star Mine, Mammoth, Tintic Mining District, Juab County, Utah, USA, raisaite occurs
with its paramorph,
pararaisaite. The raisaite crystals are well defined and
euhedral, in contrast to the fibrous masses from the type locality
(MinRec 55.2.220).
Raisite from the Upper Dumps - Image
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