What is a nitrate in mineralogy ?

Nitrates : definition

Nitrates constitute a subclass of the mineralogical class of "carbonates, nitrates, borates". The structure of nitrates is built on the (NO3)- group. N5+ ions, strongly charged and polarized, are each coordinated to 3 oxygen by very strong bonds. The resistance of this bond causes a decomposition by acids less easy than for carbonates.

Usually soluble in water, nitrates are minerals found in deserts and other arid regions (Egypt, Chile, Iran), where they often result from the evaporation of brines.

Nitrates are rare minerals (less than 15 species), the most important being nitronatrite, (NaNO3), and saltpeter or nitre (KNO3).