Niter

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Niter or nitre is the mineral form of potassium nitrate, KNO₃, also known as saltpeter. It is a colorless to white mineral crystallizing in the orthorhombic crystal system. It usually is found as massive encrustations and effervescent growths on cavern walls and ceilings where solutions containing alkali potassium and nitrate seep into the openings. It occasionally occurs as prismatic acicular crystal groups, and individual crystals commonly show twinning. It is most common in arid environments. It is a soft mineral equal to gypsum on the Mohs scale and has a low specific gravity of 2.1. It has refractive indices of nα=1.332, nβ=1.504, and nγ=1.504. It readily dissolves in water. It is a member of the nitronatrite group of minerals which includes other nitrates of sodium (nitratine), ammonium, barium, magnesium and others.

Niter has been known since pre-historic times. The name is from Hebrew neter, for salts derived from ashes.

In literature, Edgar Allan Poe invokes the supposed taint of nitre repeatedly in the short story "The Cask of Amontillado", in which the main character uses the nitre to his advantages, as it slowly diminishes his enemy Fortunato's health, before burying him alive as a form of vulgar revenge. (1846).