Formula: Na(NO3)
Normal nitrate, forms overgrowths on calcite quite readily, with the crystal axes of the two phases
ordinarily parallel; it also forms oriented growths on muscovite,
dolomite and barytocalcite
(Mindat).
Crystal System: Trigonal
Specific gravity: 2.24 to 2.29
Hardness: 1½ to 2
Streak: White
Colour: Colourless, white, lightly tinted by impurities (red-brown, grey, yellowish); colourless in transmitted light
Solubility: Slightly deliquescent. Readily soluble in water.
Melting Point 306.8oC
Environments
Nitratine is found as an efflorescence in hot dry regions; it occurs principally in bedded deposits formed in playas, in caves, and deposited
from seeping groundwater leaching nitrates from overlying rocks, especially in very dry and cold climates. Associated minerals include
niter, nitrocalcite,
epsomite, mirabilite,
halite and gypsum
(HOM, Webmin, Mindat).
Localities
The only significant deposits of nitratine occur in a belt about 450 miles long in the virtually rainless deserts
of northern Chile. The deposits consist of a near-surface layer from a few inches to a few feet thick, containing
gypsum,
halite and many other salts
(Dana).
At the type locality, Tarapacá, Chile, nitratine is associated with
polyhalite,
lautarite, halite,
gypsum, glauberite,
dietzeite, darapskite,
blödite and anhydrite
(Mindat).
At the Aqua Fria Mountain, Brewster county, Texas, US, nitratine occurs in veinlets in
trachyte
(Dana).
Near Holmdale, Owyhee county, Utah, US, nitratine occurs in veinlets in
rhyolite
(Dana).
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