Brochantite, basic copper sulphate,
Formula Cu₄SO₄(OH)₆.

Crystal system: Monoclinic.(crystals are uncommon, occurs mostly as fine needles.)
Hardness: 3.5 to 4
Density: 4.0 gms/cm³
Colour: Bright green to greenish-black.
Streak: Pale green

Brochantite occurs in the oxydation zones of copper deposits. It is frequently found in association with Malachite and Chrysocolla. It is difficult to distinguish between Brochantite and Antlerite which occurs in the same locations and has similar appearance except that its crystal system is orthorhombic.

The picture shows a vugh filled with dark green needles of Brochantite surrounded by pale blue acicular crystals of Cyanotrichite (basic copper aluminium sulphate). The specimen shown comes from La Vieja Mine, Potrerillos, Copiapo District, Chile.