nitre

{{Infobox mineral | name = Niter | category = Nitrates, oxide mineral | boxwidth = | boxbgcolor = | image = Niter from Tarapaca, Chile (cropped).jpg | caption = A piece of niter collected in Tarapaca, Chile | formula = KNO3 | IMAsymbol = Nit | molweight = | strunz = 5.NA.10 | dana = 18.1.2.1 | system = Orthorhombic | class = Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) | symmetry = Cmc21 | color = White | habit = Druse or acicular | cleavage = Very good on {001}; good on {010} | fracture = Brittle | mohs = 2 | luster = Vitreous | refractive = | opticalprop = | birefringence = | pleochroism = | streak = White | gravity = 2.10 (calc.) | melt = | fusibility = | diagnostic = | solubility = Soluble | diaphaneity = Transparent | other = | references = }}

Niter or nitre is the mineral form of potassium nitrate, KNO3. It is a soft, white, highly soluble mineral found primarily in arid climates or cave deposits.