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Formula: CuAgSe
Selenide
Specific gravity: 7.6 to 7.8
Hardness: 2½
Streak: Grey-white
Colour: Brilliant creamy white, tarnishes to bright orange
Environments
Eucairite is widely distributed in selenium deposits of hydrothermal origin,
with other selenides. Associated minerals include
berzelianite, weissite,
crookesite, clausthalite,
umangite, klockmannite,
tiemannite, chalcomenite,
malachite and calcite
(HOM, Mindat).
Localities
At Sierra de Umango, Villa Castelli, General Lamadrid department, La Rioja Province, Argentina, eucairite has been reported
in a highly altered copper ore specimen associated with umangite,
chalcomenite and malachite
(AM 35.345), but according to Mindat (accessed November 2020) this is erroneous.
At the type locality, the Skrikerum mine, Valdemarsvik, Östergötland County, Sweden, eucairite has been found as disseminated
blebs with severely tarnished surfaces in a serpentinised
gangue of quartz and
calcite
(AM 35.345).
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