Formula: Cu₂(OH)₃Cl

Species: Halides

Colour: Bright green, dark emerald-green to blackish green; shades of green in transmitted light.

Lustre: Adamantine, Vitreous

Hardness: 3 – 3½

Specific Gravity: 3.745 – 3.776

Crystal System: Orthorhombic

Name: Named in 1802 by Dmitri de Gallitzin after the type locality, in the Atacama Desert of northern Chile.

Type Locality: Atacama – Chile

Polymorph of: Botallackite, Clinoatacamite

A secondary copper mineral formed through the oxidation of other copper minerals, especially in arid, saline conditions. May be confused with brochantite.
May alter to malachite and chrysocolla, creating pseudomorphs.