Botallackite

Botallackite, chemical formula Cu2[(OH)3|Cl] is a secondary copper mineral, named for its type locality at the Botallack mine, St Just in Penwith, Cornwall. It is polymorphous with Atacamite, Paratacamite and Clinoatacamite.

In the monoclinic crystal system, Botallackite is mountain-green to green in colour, with one distinct to good cleavage.

Botallackite forms in copper deposits exposed to weathering and salt water.