Selenite, orthorhombic paramorph of clinochalcomenite, which is monoclinic
Specific gravity: 3.35
Hardness: 2 to 2½
Streak: Light blue
Colour: Intense blue, pale blue in transmitted light
Solubility: Soluble in acids
Chalcomenite is a rare secondary mineral in oxidised
copper-selenium bearing deposits
At the type locality, Cerro de Cacheuta, Sierra de Cacheuta, Cacheuta, Luján de Cuyo department, Mendoza Province, Argentina, chalcomenite is associated with umangite, clausthalite, molybdomenite and schmiederite (HOM).
At the El Dragón mine, Antonio Quijarro Province, Potosí, Bolivia, chalcomenite is associated with allophane, felsőbányaite, malachite and clinochalcomenite (HOM).
At the Hiaco mine, Pakajake Canyon, Chayanta Province, Potosí, Bolivia, chalcomenite is associated with penroseite, cobaltomenite and molybdomenite (HOM).
At the Musonoi Mine, Kolwezi, Kolwezi mining district, Lualaba, DR Congo (Zaire), chalcomenite is associated with guilleminite, derriksite and other selenites (Dana).
At cliffs near Ballybunnion, Kerry County, Munster, Ireland, a hand-sized specimen of carbon-rich black shale has been found with two fractures hosting isolated crystals, radiating groups and crude dendrites of bright blue chalcomenite. A white to pale green encrustation of mandarinoite surrounds most of the chalcomenite, completely replacing some crystals. There are a few other minerals on the specimen, tiny crystalline aggregates of a sodium iron sulphate, possibly sideronatrite, metasideronatrite, jarosite or natrojarosite, and extremely small pale green spheroidal aggregates of a copper chloride, most likely atacamite, and efflorescences of what is probably gypsum (JRS 19.35-39).
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