What is Umohoite?
Umohoite is a hydrated uranium molybdate, usually dark green to black and found as a secondary mineral in oxidised uranium-molybdenum deposits.
Mineralogy and structure
Reference formula: UMoO6·2H2O. Umohoite is triclinic and hydrated. The exact COD 9004563 model is used for the structure page; water content and alteration can vary in natural material. It is radioactive and should be treated as a controlled ore specimen. Umohoite is classified with molybdates and has triclinic crystal symmetry. Typical hardness is 2–3 on the Mohs scale and specific gravity is approximately 4.0–4.5.
Colour, lustre and habit
Typical colours include greenish-black, black, dark green, brown. The usual platy, scaly, crusty habit and sub-metallic, pearly, dull lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Umohoite forms in or is associated with oxidised uranium-molybdenum veins, mine workings, fractures and molybdate-rich alteration zones. Important documented localities include the United States, Germany, the Czech Republic, France and Australia.
Dark molybdate chemistry in a uranium mine
Umohoite is a specialist species for collectors of uranium minerals and molybdate chemistry. Dark colour, platy texture and a documented paragenesis tell a more reliable story than appearance alone.
Collecting and care
Radioactive and fragile: keep sealed and dry, avoid dust, water and heat, and use appropriate radiation-safety procedures.
