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KNO3 crystal.jpg
A niter crystal under a polarizing microscope
CategoryNitrates, oxide mineral
(repeating unit)
Strunz classification5.NA.10
Dana classification18.1.2.1
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupCmc21
Crystal habitDruse or acicular
CleavageVery good on {001}; good on {010}
Mohs scale hardness2
Specific gravity2.10 (calc.)

Niter or nitre,[4] also known as saltpeter or saltpetre, is the mineral form of potassium nitrate, KNO3 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.


Niter 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. Niter and other nitrates can also form in association with deposits of guano and similar organic materials.


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

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 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).[5]

A term (ἀφρόνιτρον, aphronitron or Aphronitre) 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.[6]

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.

On November 13 1862, the Confederate government advertised in the Charleston Daily Courier for 20 or 30 “able bodied Negro men” to work in the new nitre beds at Ashley Ferry, S.C. The nitre beds were large rectangles of rotted manure and straw, moistened weekly with urine, “dung water,” and liquid from privies, cesspools and drains, and turned over regularly. The process was designed to yield saltpeter, an ingredient of gunpowder, which the Confederate army needed during the Civil War. The National Archives published payroll records that account for more than 29,000 people compelled to such labor in the state of Virginia. The South was so desperate for saltpeter for gunpowder that one Alabama official reportedly placed a newspaper ad asking that the contents of chamber pots be saved for collection. In South Carolina, in April 1864, the Confederate government forced 31 enslaved people to work at the Ashley Ferry Nitre Works, outside Charleston.[7]


Because of its ready solubility in water, niter is most often found in arid environments and often in conjunction with other soluble minerals like halides, iodates, borates, gypsum, and rarer carbonates and sulphates. A major source of sodium nitrate mineral ("Chile saltpeter" or 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.

Niter occurs naturally in certain places like the "Caves of Salnitre" (Collbató) known since the Neolithic. In the "Cova del Rat Penat", guano (bat excrements) deposited over thousands of years became saltpeter after being leached by the action of rainwater.

In 1783, Giuseppe Maria Giovene and Alberto Fortis together discovered a "natural nitrary" in a doline close to Molfetta, Italy, named Pulo di Molfetta. The two scientists discovered that niter formed inside the walls of the caves of the doline, under certain conditions of humidity and temperature.[8] After the discovery, it was suggested that manure could be used for agriculture, in order to increase the production, rather than to make gunpowder.[9] The discovery was initially challenged by some scholars. Subsequently, chemist Giuseppe Vairo and his pupil Antonio Pitaro confirmed the discovery. Subsequently, naturalists sent by academies from all Europe came in large number to visit the site, since the niter was a fundamental ingredient in the production of gunpowder and these deposits were of considerable strategic interest.[10] Soon, the government started extraction. Short thereafter, Giovene discovered that niter also formed in other caves of Apulia.[11][12] Today the doline still contains the remains of the ancient plant used to extract the mineral, making it a site of industrial archaeology. Pulo di Molfetta is currently not open to tourists.[13]


A typical nitrary (Germany, circa 1580) with leaching deposits (C) filled with decaying vegetal material mixed with manure. A worker collects effloresced saltpeter from deposits, transporting it then to be concentrated in the factory (A) boilers.

Niter is produced in a nitrary.[14]

The process involved burial of excrements (human or animal) in the fields prepared for that purpose beside the nitraries, watering them and waiting until the leaching process did its job; after a certain time, operators gathered the saltpeter that "came out" to the ground surface by efflorescence. Then they transported it to be concentrated by ebullition in the boiler plant.[15][16]

Besides "Montepellusanus",[17] during the thirteenth century (and beyond) the only supply of saltpeter across Christian Europe (according to "De Alchimia" in 3 manuscripts of Michael Scot, 1180–1236) was "found in Spain in Aragon in a certain mountain near the sea."[18][17][19]

In 1561, Elizabeth I of England at war with Philip II of Spain, became unable to import the saltpeter (of which the Kingdom of England had no home production), and had to pay "300 pounds gold" to the German captain Gerrard Honrik for the manual "Instructions for making salpeter to growe" (the secret of the "Feuerwerkbuch" -the nitraries-).[20]

Similar minerals[edit]

Related minerals are soda niter (sodium nitrate), ammonia niter or gwihabaite (ammonium nitrate), nitrostrontianite (strontium nitrate), nitrocalcite (calcium nitrate), nitromagnesite (magnesium nitrate), nitrobarite (barium nitrate) and two copper nitrates, gerhardtite and buttgenbachite; in fact all of the natural elements in the first three columns of the periodic table and numerous other cations form nitrates which are uncommonly found for the reasons given, but have been described. 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.

See also[edit]


  1. ^ "Niter Mineral Data".
  2. ^ "Niter: Mineral information, data and localities".
  3. ^ Adiwidjaja, G.; Pohl, D. (2003), "Superstructure of α-phase potassium nitrate", Acta Crystallogr. C, 59 (12): 1139–40, doi:10.1107/S0108270103025277, PMID 14671340.
  4. ^ "Definition of nitre". Merriam-Webster. Retrieved March 11, 2016.
  5. ^ "neter and nitrogen".
  6. ^ More conventional soap also appears in the accounts but was more expensive: John Matthews, The Journey of Theophanes, Yale UP 2006
  7. ^ Ruane, Michael. "During the Civil War, the enslaved were given an especially odious job. The pay went to their owners". Washington Post. Retrieved July 10, 2020.
  8. ^ necrologio-giovene, pag. 39
  9. ^ "Opuscoli scelti sulle scienze e sulle arti tratti dagli Atti delle Accademie, e dalle altre Collezioni filosofiche, e letterarie, e dalle opere più recenti inglesi, tedesche, francesi, latine, e italiane, e da manoscritti originali, e inediti: 12". 1789.
  10. ^ elogio-storico, pagg. 8-10
  11. ^ elogio-storico, pagg. 9-10
  12. ^ lettera-a-fortis-1784
  14. ^ John Spencer Bassett; Edwin Mims; William Henry Glasson; William Preston Few; William Kenneth Boyd; William Hane Wannamaker (1904). The South Atlantic Quarterly. Duke University Press. Retrieved February 22, 2013.
  15. ^ Paul-Antoine Cap (1857). Etudes biographiques pour servir à l'histoire des sciences ...: sér. Chimistes. V. Masson. pp. 294–. Retrieved February 23, 2013.
  16. ^ Oscar Gutman (1906). Monumenta pulveris pyrii. Repr. Artists Press Balham. pp. 50–.
  17. ^ a b James Riddick Partington (1960). A history of Greek fire and. JHU Press. pp. 89 –. ISBN 978-0-8018-5954-0.
  18. ^ James Riddick Partington (1960). A history of Greek fire and March 2012. JHU Press. pp. 311 –. ISBN 978-0-8018-5954-0.
  19. ^ Alexander Adam (1805). A compendious dictionary of the Latin tongue: for the use of public Seminar and private March 2012. Printed for T. Cachorro and W. Davies, by C. Stewart, London, Bell and Bradfute, W. Creech.
  20. ^ SP Dom Elizabeth vol.xvi 29-30 (1589)

Further reading[edit]

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