What is Ullmannite?
Ullmannite is a nickel antimony sulfide, usually steel-grey and metallic, and a characteristic mineral of hydrothermal nickel-antimony ore veins.
Mineralogy and structure
Reference formula: NiSbS. Ullmannite has a cubic structure related to the cobaltite-gersdorffite group. The exact COD 1536521 entry is used for the model; natural substitutions and intergrowths are common. Ullmannite is classified with sulfosalts and has cubic crystal symmetry. Typical hardness is 5.5–6 on the Mohs scale and specific gravity is approximately 5.6–6.0.
Colour, lustre and habit
Typical colours include tin-white, steel-grey, black, iridescent. The usual cubic, granular, massive habit and metallic lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Ullmannite forms in or is associated with hydrothermal sulfide veins, cobalt-nickel deposits and antimony-rich ore systems. Important documented localities include Germany, the Czech Republic, Canada, Morocco, Sweden and the United States.
Metallic grey geometry from a nickel ore vein
Ullmannite is a compact record of nickel and antimony transport in hydrothermal systems. Sharp cubic crystals and a documented association are more informative than surface colour alone.
Collecting and care
Keep dry and enclosed, avoid dust and acids, and wash hands after handling. Do not grind or polish sulfide ore without professional ventilation and controls.
