What is Nitratine?
Nitratine is sodium nitrate, a soft trigonal evaporite and one of the characteristic minerals of Chilean nitrate deposits.
Mineralogy and crystal structure
Reference formula: NaNO3. Nitratine is the trigonal nitrate analogue of calcite and is highly soluble in water. Its softness, salty taste historically reported in field work and nitrate-rich setting require careful, non-destructive identification. Nitratine is classified with nitrates and has a trigonal crystal system. Typical hardness is 1.5–2 on the Mohs scale and specific gravity is approximately 2.2–2.3.
Colour, lustre and habit
Typical colours include colourless, white, grey, brown. The usual rhombohedral, granular, crusty habit and vitreous, pearly lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Nitratine forms in or is associated with arid nitrate soils, caliche horizons, salt crusts and cave or guano-related deposits. Important documented localities include Chile, Peru, Bolivia, Egypt, South Africa and the United States.
A white crust from the Atacama nitrate fields
Nitratine is inseparable from the landscape that made it: arid evaporation concentrates sodium nitrate into crusts that can later dissolve almost as quickly as they formed.
Collecting and care
Keep dry, avoid water and acids, and do not taste a specimen; protect from abrasion.
