Atacamite MMT 318 from Copiapo,
Chile; Mina Farola
CHEMISTRY - Cu2(OH)3Cl
CRYSTALLOGRAPHY - Orthorhombic; dipyramidal
CRYSTAL GROWTH AND HABITS - Usually found as long, slender prismatic crystals or tabular. It often forms crystalline aggregates, sometimes divergent; also fibrous or granular.
COLOR AND OPTICAL PROPERTIES - Normally some shade of green - from bright green to blackish green.
HARDNESS - 3 - 3.5
SPECIFIC GRAVITY - 3.7 - 3.8
LUSTER - Adamantine to vitreous
STREAK - Light green
BREAKABILITY - Very good cleavage {010} and fair along {101} with an otherwise conchoidal fracture. Brittle.
OCCURRENCE - Atacamite is a secondary mineral formed by the alteration of other copper minerals - especially in arid, saline conditions.
ASSOCIATED MINERALS - Malachite, Cuprite, Brochantite, Chrysocolla, Gypsum, Limonite.
MINERAL NAME - From where it was first found in the Atacama Desert of northern Chile.