Very soluble mineral, NaNO3; sp. gr. 2.2–2.3; hardness 1–2; trigonal; normally colourless or white, with various darker colours due to impurities; white streak; vitreous lustre; crystals rhombohedral, also occurs massive; cleavage perfect, rhombohedral; occurs in arid regions as surface deposits together with gypsum, halite, and other soluble nitrates and sulphates; deliquescent. It is worked as a source of nitrate.