What is Omeiite?
Omeiite is an exceptionally dense osmium arsenide, a rare platinum-group mineral from highly specialised ore and placer environments.
Mineralogy and crystal structure
Reference formula: OsAs. Omeiite is an orthorhombic arsenide with very high density. Natural grains are usually microscopic and chemically variable; professional analysis is required for reliable identification. Omeiite is classified with arsenides and has a orthorhombic crystal system. Typical hardness is 5.5–6 on the Mohs scale and specific gravity is approximately 10.0–10.5.
Colour, lustre and habit
Typical colours include grey, black, silver-grey. The usual granular, massive, crystalline habit and metallic lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Omeiite forms in or is associated with platinum-group element deposits, ultramafic rocks and placer concentrates. Important documented localities include China, Russia, South Africa and other platinum-group districts.
Extreme density in a microscopic grain
Omeiite demonstrates how unusual elements can hide in ordinary-looking dark grains. Its osmium-rich chemistry makes it a valuable clue to platinum-group mineralisation.
Collecting and care
Keep enclosed and avoid dust, cutting and casual testing; preserve the original concentrate and provenance.
