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Category Nitrate mineral
(repeating unit)
Strunz classification 5/A.01-10
Crystal symmetry Trigonal 32/m
Unit cell a = 5.06 Å, c = 16.82 Å
Formula mass 84.99 gm
Color Colorless, White, Gray, Yellowish, Brownish
Crystal habit Granular - Generally occurs as anhedral to subhedral crystals in matrix; Massive - Uniformly indistinguishable crystals forming large masses.
Crystal system Trigonal hexagonal scalenohedral (32/m), Space Group (R3 2/c)
Cleavage {???} Perfect
Fracture Sectile - Curved shavings or scrapings produced by a knife blade,
Tenacity Sectile
Mohs scale hardness 1.5 - 2
Luster Vitreous (Glassy)
Streak White
Diaphaneity Transparent
Specific gravity 2.26
Optical properties Uniaxial (-)
Refractive index nω = 1.580 - 1.587 nε = 1.330 - 1.336
Birefringence δ = 0.250-0.251
Solubility Readily soluble in water
Other characteristics Slightly deliquescent
References [1][2]

Nitratine (also nitratite), also known as cubic niter (UK: nitre), soda niter or Chile saltpeter (UK: Chile saltpetre), is a mineral, the naturally occurring form of sodium nitrate, NaNO3. Chemically it is the sodium analogue of saltpeter. Nitratine crystallizes in the trigonal system, but rarely occurs as well formed crystals. It is isostructural with calcite. It is quite soft and light with a Mohs hardness of 1.5 to 2 and a specific gravity of 2.24 to 2.29. Its refractive indices are nω=1.587 and nε=1.336.[3]

The typical form is as coatings of white, grey to yellowish brown masses. The rare crystals when found typically have the scalenohedral form of the calcite structure. It is found only as an efflorescence in very dry environments. It is very soluble in water such that it is deliquescent and will absorb water out of the air and turn into a puddle of sodium nitrate solution when exposed to humid air.

Nitratine was once an important source of nitrates for fertilizer and other chemical uses including fireworks. It has been known since 1845 from occurrences in the Confidence Hills, Southern Death Valley, California and the Atacama Desert, Chile.

See also[edit]


  1. ^ Nitratine page on
  2. ^ Nitratine page on
  3. ^ Nesse, W, introduction to Optical Mineralogy, Fourth Edition (Oxford, New York, Oxford University Press) 2013. appendix II, B.3