Selma's Confederate Nitre Works procured niter for gunpowder from limestone caves.
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Other solid deposits include halite, amphibole, cryolite, soda niter, and zeolite.
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It occurs as a mineral niter and is a natural solid source of nitrogen.
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The mineral form is also known as nitratine, nitratite or soda niter.
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As a result, to this day its ingredients remain a matter of much speculation and debate, with proposals including naphtha, quicklime, sulphur, and niter.
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More examples
Potassium nitrate: (KNO3) used especially as a fertilizer and explosive
Niter (US) or nitre (UK) is the mineral form of potassium nitrate, KNO3, also known as saltpeter (US) or saltpetre (UK). ...