What is Smithsonite?
Smithsonite is a colourful zinc carbonate, famous for blue-green botryoidal crusts and exceptional collector specimens from oxidised zinc deposits.
Mineralogy and crystal structure
Reference formula: ZnCO3. Smithsonite is trigonal and belongs to the calcite group. Trace copper, cobalt, cadmium and other elements can produce striking colour, but locality and analysis are important for species-level identification. Smithsonite is classified with carbonates and has a trigonal crystal system. Typical hardness is 4–4.5 on the Mohs scale and specific gravity is approximately 4.3–4.5.
Colour, lustre and habit
Typical colours include blue, green, pink, yellow, brown, white. The usual botryoidal, reniform, granular habit and vitreous, pearly, silky lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Smithsonite forms in or is associated with supergene oxidation zones above zinc sulphide deposits, cavities and carbonate-rich host rocks. Important documented localities include Namibia, Greece, Mexico, the United States, Australia and Italy.
Botryoidal colour in an oxidised zinc deposit
Smithsonite sells through colour, texture and locality. A blue-green botryoidal crust from a famous mine can be both a refined décor object and a precise record of supergene chemistry.
Collecting and care
Protect from scratches and acids. Clean gently with water and a soft brush; avoid vinegar, abrasive polishing and prolonged soaking.
