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Formula: TlAs5S8
Sulphosalt, thallium- and
arsenic- bearing mineral
Crystal System: Monoclinic
Specific gravity: 4.5 measured, 4.105 calculated
Hardness: 2
Streak: Deep red
Colour: Black
Environments
Bernardite occurs in hydrothermal veins in
thallium - arsenic deposits. Common
associates include edenharterite,
erniggliite, hatchite,
hutchinsonite, lorándite,
orpiment, realgar,
stalderite and wallisite
(Mindat).
Localities
At the type locality, Allchar, Rožden, Kavadarci Municipality, North Macedonia, bernardite occurs in the
thallium-bearing deposit with
realgar and orpiment. It forms
black, thick-tabular crystals that are typically less than 1 mm, but up to 4 mm in size; faces are dull, partly
corroded and striated
(AM 75.1209).
At the Lengenbach Quarry, Fäld, Binn, Goms, Valais, Switzerland, bernardite occurs in a hydrothermal deposit
with other arsenic-thallium
sulphides. Associated minerals include
realgar, orpiment,
hutchinsonite, wallisite,
hatchite, lorándite,
edenharterite, erniggliite
and stalderite
(HOM).
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