What is Chalcanthite?
Chalcanthite is a vivid blue hydrated copper sulfate, famous for transparent blue crystals and efflorescent crusts in arid mine workings.
Mineralogy and structure
The reference formula is CuSO4·5H2O. Chalcanthite belongs to the sulfates and has a triclinic crystal system. Its triclinic structure contains five water molecules per formula unit. Chalcanthite is water-soluble and should be kept dry; it is a display mineral rather than a material for jewellery.
Colour and appearance
Typical colours include bright blue, azure blue, blue-green. Crystal habit, lustre, transparency and matrix association are often as diagnostic as colour.
Formation and localities
Chalcanthite forms in or is associated with oxidised copper deposits, mine galleries and evaporation zones where copper sulfate solutions crystallise. Important documented localities include Chuquicamata in Chile, Bisbee in Arizona, the Democratic Republic of the Congo and historic European mines.
Collecting and care
Chalcanthite 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.
