1 Photos
Nitre
Chemical Formula	KNO3
Species	Nitrates
Crystal System	Orthorhombic
Mohs Scale	2
Specific Gravity	2.10
Color	white
Streak	white
Luster	vitreous
Refractive Index	nα = 1.332nβ = 1.504nγ = 1.504
Diaphaneity	transparent
Cleavage	very good on ; good on
Fracture	brittle
Crystal Habit：druse or acicular

Niter (American English) or nitre (most English-speaking countries) is the mineral form of potassium nitrate, KNO₃, also known as saltpeter in America or saltpetre in other English speaking countries. Historically, the term "niter" – cognate with "natrium", a Latin word for sodium – has been very vaguely defined, and it has been applied to a variety of other minerals and chemical compounds, including sodium nitrate (also "soda niter", "cubic niter", or nitratine), sodium carbonate and potassium carbonate.

Because of its ready solubility in water, niter is most often found in arid environments. A major source of sodium nitrate mineral ("Chile saltpeter", that is, nitratine) is the Atacama desert in Chile. Potassium and other nitrates are of great importance for use in fertilizers, and, historically, gunpowder. Much of the world's demand is now met by synthetically produced nitrates, though the natural mineral is still mined and is still of significant commercial value.

Description

Niter is a colorless to white mineral crystallizing in the orthorhombic crystal system. It usually is found as massive encrustations and effervescent growths on cavern walls and ceilings where solutions containing alkali potassium and nitrate seep into the openings. It occasionally occurs as prismatic acicular crystal groups, and individual crystals commonly show twinning.

History

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. The name is from the Greek νιτρων nitron from Ancient Egyptian netjeri, related to the Hebrew néter, for salt-derived ashes (their interrelationship is not clear).

The Hebrew néter may have been used as, or in conjunction with soap, as implied by Jeremiah 2:22, "For though thou wash me with nitre, and take thee much sope…" However, it is not certain which substance (or substances) the Biblical "neter" refers to, with some suggesting sodium carbonate. Indeed, the Neo Latin word for sodium natrium is derived from this same class of desert minerals called natron (French) from Spanish natrón through Greek νιτρων (nitron), derived from Ancient Egyptian netjeri, referring to the carbonate sodium 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).

A term (?φρ?νιτρον) which translates as "foam of niter" was a regular purchase in a fourth-century AD series of financial accounts, and since it was expressed as being "for the baths" was probably used as soap.

Niter was used to refer specifically to nitrated salts known as various types of saltpeter (only nitrated salts were good for making gunpowder) by the time niter and its derivative nitric acid were first used to name the element nitrogen, in 1790.