What is Chalcocite?
Chalcocite is a copper sulfide and an important high-grade copper ore, recognised by its dark metallic appearance and soft, heavy character.
Mineralogy and structure
The reference formula is Cu2S. Chalcocite belongs to the sulfides and has a monoclinic crystal system. Chalcocite has a monoclinic structure at ordinary temperature, with temperature-dependent structural transitions. It commonly occurs with covellite, bornite, malachite and native copper.
Colour and appearance
Typical colours include dark grey, black, lead-grey. Crystal habit, lustre, transparency and matrix association are often as diagnostic as colour.
Formation and localities
Chalcocite forms in or is associated with secondary enrichment zones below the oxidised caps of copper deposits. Important documented localities include Cornwall, Chile, Mexico, the United States and other major porphyry and sediment-hosted copper districts.
Collecting and care
Chalcocite is best kept as a labelled collector or reference specimen. Protect fragile crystals from impact and prolonged humidity changes. Lead-, arsenic-, chromium- and cobalt-bearing minerals should not be cut, ground or used in jewellery.
