What is Oxammite?
Oxammite is a rare ammonium iron sulfate hydrate found in guano-influenced or fumarolic environments, where soluble salts crystallise from acidic fluids.
Mineralogy and crystal structure
Reference formula: (NH4)2Fe2+(SO4)2·6H2O. Oxammite is hydrated and soluble; humidity, temperature and oxidation can change its composition. The orthorhombic COD model represents one hydrated state. Oxammite is classified with sulfates and has a orthorhombic crystal system. Typical hardness is 2–3 on the Mohs scale and specific gravity is approximately 1.8–2.0.
Colour, lustre and habit
Typical colours include colourless, white, pale green, yellow. The usual prismatic, crystalline, crusty habit and vitreous, pearly lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Oxammite forms in or is associated with fumaroles, guano deposits and acidic evaporative environments rich in ammonium and iron. Important documented localities include Vesuvius in Italy, the Galápagos, Chile, Peru and other volcanic or guano localities.
A fragile salt from acidic vapours
Oxammite is a mineral of evaporation and chemistry in motion. Its ammonium-bearing sulfate lattice forms where volcanic gases, iron and water meet, then can disappear when humidity changes.
Collecting and care
Keep sealed, cool and dry; avoid water, heat, dust and prolonged skin contact.
