The Neo-Latin word for sodium, natrium, is derived from this same class of desert minerals called natron (French) from Spanish natrón through Greek νίτρον ( nitron), derived from Ancient Egyptian netjeri, referring to the sodium carbonate salts occurring in the deserts of Egypt, not the nitrated sodium salts typically occurring in the deserts of Chile (classically known as " Chilean saltpeter" and variants of this term). The Hebrew néter may have been used as, or in conjunction with soap, as implied by Jeremiah 2:22, "For though thou wash thee with niter, and take thee much soap." However, it is not certain which substance (or substances) the Biblical "neter" refers to, with some suggesting sodium carbonate. The name is from the Ancient Greek νιτρων nitron from Ancient Egyptian netjeri, related to the Hebrew néter, for salt-derived ashes (their interrelationship is not clear).
Niter as a term has been known since ancient times, although there is much historical confusion with natron (an impure sodium carbonate/bicarbonate), and not all of the ancient salts known by this name or similar names in the ancient world contained nitrate. Niter and other nitrates can also form in association with deposits of guano and similar organic materials. It occasionally occurs as prismatic acicular crystal groups, and individual crystals commonly show pseudohexagonal twinning on. It occurs in the soils of arid regions and as massive encrustations and efflorescent growths on cavern walls and ceilings where solutions containing alkali potassium and nitrate seep into the openings. Its crystal structure resembles that of aragonite, with potassium replacing calcium and nitrate replacing carbonate. It is the mineral form of potassium nitrate, KNO 3, and is soft ( Mohs hardness 2), highly soluble in water, and easily fusible. Niter is a colorless to white mineral crystallizing in the orthorhombic crystal system. Historically, the term niter was not well differentiated from natron, both of which have been very vaguely defined but generally refer to compounds of sodium or potassium joined with carbonate or nitrate ions. It is a soft, white, highly soluble mineral found primarily in arid climates or cave deposits. Niter or nitre is the mineral form of potassium nitrate, KNO 3.
A niter crystal under a polarizing microscope
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