|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)|
|Fracture||Sectile - Curved shavings or scrapings produced by a knife blade,|
|Mohs scale hardness||1.5 - 2|
|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|
Nitratine (also nitratite), also known as cubic niter (UK: nitre), soda niter or Chile saltpeter (UK: saltpetre), is a mineral, the naturally occurring form of sodium nitrate, NaNO3. Chemically it is the Na-analogue of niter. 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.
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 It has since been replaced by fixed nitrogen from the air as the main source of nitrogen. It has been known since 1845 from occurrences in the Confidence Hills, Southern Death Valley, California and the Atacama Desert, Chile.
See also 
- Nitratine page on mindat.org
- Nitratine page on webmineral.com
- Nesse, W, introduction to Optical Mineralogy, Fourth Edition (Oxford, New York, Oxford University Press) 2013. appendix II, B.3
|This article about a specific mineral or mineraloid is a stub. You can help Wikipedia by expanding it.|