Atacamite

Formula:  Cu₂Cl(OH)₃

Origin of name:  Locality; Atacama Desert., Chile

Crystal system:  Orthorhombic

Crystal class:  2/m 2/m 2/m

Twinning:  On {110} rare, contact or penetration (doublets, trillings), about [544] more common

Unit cell: a = 6.030 Å, b = 9.122 Å, c = 6.868 Å

Colour:  Bright to dark green

Diaphaneity: Transparent to translucent

Luster:  Vitreous to adamantine

Habit:  Crystals slender prismatic; tabular; often striated; crusts of subparallel crystals; massive, granular

Hardness:  3 to 3.5

Specific gravity:  3.75 to 3.78

Cleavage:  2; {010} perfect, {101} fair

Tenacity: Brittle

Streak:  Apple-green

Synonyms/varieties: Paratacamite

Comments:  Trimorphous with paratacamite, clinoatacamite and botallackite. found as an oxidation product of other copper minerals, especially under arid, saline conditions; in fumarolic deposits; as a weathering product of sulphides in subsea black smoker deposits; an alteration of bronze and copper objects of antiquity.