a class of minerals that are natural salts of nitric acid. The main natural nitrate minerals are sodium nitrate (Chile saltpeter), NaNO3; potassium nitrate, KNO3; ammonium nitrate, NH4NO3; darapskite, Na3(NO3) · (SO4) · H2O; nitromagnesite, Mg(NO3)2 · 6H2O; nitrocalcite, Ca(NO3)2 · 4H2O; nitrobarite, Ba(NO3)2; gerhardtite, Cu2(NO3)(OH)3; lycasite, Cu6(NO3)2 · (PO4)(OH)7, and buttgenbachite, Cu19-(NO3)2 · (OH)32Cl4 · 3H2O.
The structure of natural nitrates is similar to that of natural carbonates but is less stable because of the high degree of polarization of oxygen atoms under the action of pentavalent nitrogen.
Natural nitrates are encountered in the form of saltlike masses, efflorescences, incrustations, and coatings. All nitrates are highly soluble in water and have a cooling taste. Significant deposits of natural nitrates are found in Chile (Tarapacá and Antofagasta provinces), where the minerals are associated with halides, sulfates, selenates, and some iodates. In these deposits, potassium nitrate and sodium nitrate make up the main reserves.
Alkaline natural nitrates are often formed by the reaction of organic nitrates and alkaline salts (for example, coatings of potassium nitrate and sodium nitrate in rock cavities and fissures and in rock fragments).
As of 1974 there was only limited mining of natural nitrates; most nitrogen compounds were produced chemically (by synthesis of ammonia from atmospheric nitrogen and hydrogen).
REFERENCEKostov, I. Mineralogiia. Moscow, 1971. (Translated from English.)
M. D. DORFMAN