Niter, a mineral with the formula KNO3, often found in dry or arid regions — Photo: Shannon Heinle · CC0
Niter
Also known as: Saltpeter, Nitre.
Natural potassium nitrate — saltpeter — a soft white soluble mineral of caves and arid soils, historically vital for gunpowder.
Intro adapted from Wikipedia (CC BY-SA).
Niter is an IMA-recognized mineral species in the nitrate class, with the chemical formula K(NO₃).
It crystallizes in the orthorhombic crystal system (space group Cmc2_1).
Key properties: Mohs hardness 2; specific gravity 2.109; typically colorless or white or gray; White streak; Vitreous luster; refractive index 1.447; optically biaxial.
IMA symbol Nit, grandfathered status — known before the IMA’s founding.
Found in some caves, typically formed by bacterial action on animal matter, as bat guano, or from vegetable matter, such as humus, exposed to seeping groundwater; an efflorescence on soils or cliff faces in arid regions.
It is found associated with Nitratine, nitrocalcite, nitromagnesite, epsomite, gypsum, calcite.
A name from antiquity, used to distinguish potassium nitrate from sodium nitrate.
Collections: Everyday Minerals.