brochantite

Brochantite is a monoclinic basic copper sulfate mineral with the chemical formula Cu4SO4(OH)6. It forms as a secondary mineral in the oxidized zones of copper sulfide deposits, typically by alteration of copper sulfates in the presence of water. The mineral is usually emerald-green to bottle-green, with a vitreous to dull luster, and occurs as tabular to acicular crystals or in fibrous, botryoidal masses. It has a hardness of about 3.5 to 4 on the Mohs scale and a relatively high specific gravity around 3.8.

Occurrence and associations are characteristic of its formation environment. Brochantite commonly appears in the oxidized portions of copper deposits alongside other secondary copper minerals such as malachite, azurite, chrysocolla, and cuprite. It has been reported in mineral localities worldwide, with notable occurrences in the United States, Chile, France, and Morocco.

Etymology and naming: the mineral is named in honor of the French mineralogist François Brochant de Villeneuve, who contributed to the study of copper minerals.

Uses and significance: brochantite is primarily of interest to mineral collectors and researchers studying copper-oxide/sulfate systems. It can occur as a component of ore assemblages in some copper deposits, but its relative rarity limits its role as an ore compared with more common copper minerals.