Nitre

"Niter" redirects here. For other meanings of the word "Niter" and "Nitre", see Niter (disambiguation).

"Saltpeter" redirects here. For other meanings of the word "Saltpeter", see Saltpeter (disambiguation).

Not to be confused with natron.

Nitre
A nitre crystal under a polarizing microscope
General
Category	Nitrates
Formula (repeating unit)	KNO3
Strunz classification	05.NA.10
Dana classification	18.1.2.1
Crystal symmetry	2/m 2/m 2/m
Identification
Color	white
Crystal habit	druse or acicular
Crystal system	orthorhombic
Cleavage	very good on {001}; good on {010}
Fracture	brittle
Mohs scale hardness	2
Luster	vitreous
Streak	white
Diaphaneity	transparent
Specific gravity	2.10 (calc.)
Refractive index	nα = 1.332 nβ = 1.504 nγ = 1.504
Solubility	soluble
References

Nitre (most English-speaking countries) or Niter (American English) is the mineral form of potassium nitrate, KNO₃, also known as saltpeter in America or saltpetre in other English-speaking countries. Historically, the term "nitre" 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. Three related minerals are soda nitre (sodium nitrate), ammonia nitre (ammonium nitrate), and strontium nitrate.

Because of its ready solubility in water, nitre 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

Nitre is a colorless to white mineral crystallizing in the orthorhombic crystal system. It usually is found as massive encrustations and efflorescent 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

Nitre 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 thee 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 νίτρον (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 (ἀφρόνιτρον) which translates as "foam of nitre" 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.

Nitre 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 nitre and its derivative nitric acid were first used to name the element nitrogen, in 1790.

See also

• Aphronitre
• Nitrary

External links

• Etymology of "nitre"
• nitre page on mindat.org
• nitre page on webmineral.com
• Mineral galleries
• Poe's The Cask of Amontillado