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Formula: Cu4(SO4)(OH)6.H2O
Hydrated sulphate containing hydroxyl
Crystal System: Monoclinic
Specific gravity: 3.32 measured, 3.35 calculated
Hardness: 2 to 3
Streak: Pale blue
Colour: Sky-blue to dark-blue, may be slightly greenish-blue
Solubility: Insoluble in ammonia
Environments:
Posnjakite is a secondary mineral formed in the oxidised zone
of copper-bearing hydrothermal mineral deposits, commonly of post-mine origin; it may occur in slags. Associated minerals
include brochantite, langite,
devilline, serpierite,
woodwardite, wroewolfeite,
aurichalcite, azurite,
malachite and chalcopyrite
(HOM). It generally forms at low temperatures
(Mindat).
Localities
At Canaveille, Pyrenees, France, posnjakite and langite
pseudomorphs after calcite have
been found
(KL p193).
At Neudorf, Harz mountains, Saxony-Anhalt, Germany, posnjakite has been discovered on material from the dumps
associated with serpierite, gypsum and
aragonite
(Minrec 43.1.40).
At the type locality, the Nura-Taldy tungsten deposit, Shet, Karaganda Region, Kazakhstan, posnjakite occurs in
quartz veins in small grains, as small tabular crystals up to 0.5 mm and as films
on fissures in quartz and fluorite. It
is associated with aurichalcite and other
secondary minerals associated with oxidising
chalcopyrite
(AM 52.1582-1583).
At Silver Gill, Caldbeck Fells, Cumbria, England, UK, posnjakite occurs with
ramsbeckite, schulenbergite
and minor dark blue linarite
(JRS 8(2).92).
At Copper Creek, Bunker Hill District, Pinal county, Arizona, USA, posnjakite occurs as clusters of tiny crystals with
orthoserpierite
(R&M 96.2.155).
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