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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.〔Nesse, W, introduction to Optical Mineralogy, Fourth Edition (Oxford, New York, Oxford University Press) 2013. appendix II, B.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== * List of Saltpeter works in Tarapacá and Antofagasta * (Nitratine page on mindat.org ) * (Nitratine page on webmineral.com ) * (Mineral galleries data ) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Nitratine」の詳細全文を読む スポンサード リンク
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