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Formula: CuAgSe
Selenide, copper- and
silver- bearing mineral
Crystal system: Orthorhombic
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 September 2025) this is erroneous, and the source of the
specimen is probably Sierra de Cacho, Villa Castelli, General Lamadrid Department, La Rioja Province, Argentina.
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).
Eucairite from the Shrikerum Mine -
Image
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