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A niter crystal under a polarizing microscope
CategoryNitrates, oxide mineral
(repeating unit)
IMA symbolNit[1]
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[5] is the mineral form of potassium nitrate, KNO3. It is a soft, white, highly soluble mineral found primarily in arid climates or cave deposits.

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 is the mineral form of potassium nitrate, KNO3,[6] and is soft (Mohs hardness 2),[7] highly soluble in water,[6] and easily fusible. Its crystal structure resembles that of aragonite, with potassium replacing calcium and nitrate replacing carbonate.[8] 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.[6] It occasionally occurs as prismatic acicular crystal groups, and individual crystals commonly show pseudohexagonal twinning on [110]. Niter and other nitrates can also form in association with deposits of guano and similar organic materials.[7]

History and etymology[edit]

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.[6] 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).[9]

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.[10]

The Neo-Latin word for sodium, natrium, is derived from this same class of desert minerals called natron (French)[11] 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).[9][12][self-published source?]

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.[13]

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.[14]


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.[15][16] 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.[17][18]

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.[citation needed]

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.[19] After the discovery, it was suggested that manure could be used for agriculture, in order to increase the production, rather than to make gunpowder.[20] The discovery was challenged by scholars until chemist Giuseppe Vairo and his pupil Antonio Pitaro confirmed the discovery. Naturalists sent by academies from all Europe came in large number to visit the site; since niter is a fundamental ingredient in the production of gunpowder, these deposits were of considerable strategic interest.[21]: 8–10  The government started extraction. Shortly thereafter, Giovene discovered that niter in other caves of Apulia.[21]: 9–10 [22] The remnants of the extraction plant is a site of industrial archaeology, although currently not open to tourists.[23]

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.[citation needed]

See also[edit]

  • Caliche – Calcium carbonate based concretion of sediment
  • Nitratine - Sodium based fertilizer


  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ "Niter Mineral Data".
  3. ^ "Niter: Mineral information, data and localities".
  4. ^ Adiwidjaja, G.; Pohl, D. (2003), "Superstructure of α-phase potassium nitrate", Acta Crystallogr. C, 59 (12): 1139–40, doi:10.1107/S0108270103025277, PMID 14671340.
  5. ^ "Definition of nitre". Merriam-Webster. Retrieved March 11, 2016.
  6. ^ a b c d Jackson, Julia A., ed. (1997). "niter". Glossary of geology (Fourth ed.). Alexandria, Virginia: American Geological Institute. ISBN 0922152349.
  7. ^ a b Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (2005). "Niter" (PDF). Handbook of Mineralogy. Mineral Data Publishing. Retrieved December 28, 2021.
  8. ^ Klein, Cornelis; Hurlbut, Cornelius S. Jr. (1993). Manual of mineralogy : (after James D. Dana) (21st ed.). New York: Wiley. p. 418. ISBN 047157452X.
  9. ^ a b "nitre". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  10. ^ Haberfield, Paul (January 1985). "What's in a name: NaNO3". Journal of Chemical Education. 62 (1): 56. Bibcode:1985JChEd..62...56H. doi:10.1021/ed062p56.
  11. ^ "natrium". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  12. ^ Curwin, David (2008). "neter and nitrogen".
  13. ^ More conventional soap also appears in the accounts but was more expensive: John Matthews, The Journey of Theophanes, Yale UP 2006
  14. ^ "nitrogen". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  15. ^ Reeves, C. C. (November 24, 1978). "Economic Significance of Playa Lake Deposits". Modern and Ancient Lake Sediments: 279–290. doi:10.1002/9781444303698.ch15. ISBN 9780632002344.
  16. ^ Ericksen, G.E. (1983). "The Chilean Nitrate Deposits: The origin of the Chilean nitrate deposits, which contain a unique group of saline minerals, has provoked lively discussion for more than 100 years". American Scientist. 71 (4): 366–374. JSTOR 27852136.
  17. ^ Barnum, Dennis W. (December 2003). "Some History of Nitrates". Journal of Chemical Education. 80 (12): 1393. Bibcode:2003JChEd..80.1393B. doi:10.1021/ed080p1393.
  18. ^ Burkhardt, John J.; Heath, Garvin A.; Turchi, Craig S. (March 15, 2011). "Life Cycle Assessment of a Parabolic Trough Concentrating Solar Power Plant and the Impacts of Key Design Alternatives". Environmental Science & Technology. 45 (6): 2457–2464. Bibcode:2011EnST...45.2457B. doi:10.1021/es1033266. PMID 21391722.
  19. ^ Pietro Filioli (1837). "Necrologia – Giuseppe Maria Giovene – Arciprete della Cattedrale Chiesa di Molfetta". Annali Civili del Regno delle Due Sicilie (in Italian). Tipografia del Real Ministero degli Affari Interni nel Reale Albergo de' Poveri. 25, gennaio e febbraio: 39.
  20. ^ "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" (in Italian). 1789.
  21. ^ a b Andrea Tripaldi (1841). "Elogio storico del canonico arciprete Giuseppe Maria Giovene". Memorie di Matematica e di Fisica della Società Italiana delle Scienze Residente in Modena (in Italian). Modena: Tipi della R. D. Camera. 22.
  22. ^ Giuseppe Maria Giovene (August 7, 1784). Lettera del Sig. canonico D. Giuseppe Maria Giovene, Vicario generale di Molfetta, al Sig. Abate Alberto Fortis, contenente varie osservazioni sulla nitrosità naturale della Puglia (in Italian). Molfetta.

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