What is Otavite?
Otavite is a cadmium carbonate of the calcite group, a rare mineral best known from oxidised polymetallic deposits such as Tsumeb.
Mineralogy and crystal structure
Reference formula: CdCO3. Otavite is isostructural with calcite, but cadmium gives it unusually high density. It may occur as tiny coatings or crystals and should not be confused with harmless carbonate look-alikes. Otavite is classified with carbonates and has a trigonal crystal system. Typical hardness is 3.5–4 on the Mohs scale and specific gravity is approximately 4.9–5.0.
Colour, lustre and habit
Typical colours include white, yellow-brown, red-brown, colourless. The usual rhombohedral, crystalline, massive habit and adamantine, vitreous lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Otavite forms in or is associated with oxidised zones of zinc-lead-copper deposits and carbonate-rich supergene environments. Important documented localities include Tsumeb in Namibia, Sardinia in Italy, Mexico, Greece and other cadmium-bearing ore districts.
A dense carbonate in the oxidation zone
Otavite shows how a familiar calcite-type structure can host a less familiar element. Cadmium-rich chemistry makes a small crystal unusually dense and scientifically valuable.
Collecting and care
Keep sealed and avoid dust; do not use for jewellery or lapidary work and wash hands after handling.
