Niter

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.

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Niter has been known since ancient times. The name is from Hebrew neuter, for salt derived ashes.

In literature, Edgar Allan Poe invokes the supposed Saint of Nitre repeatedly in the short story "The Cask of Amontillado" (1846), in which the main character uses the nitre to his "advantages", as it slowly murders his enemy. Fortunato's health worsens, until Montresor takes his revenge in the form of immurement.

References

• Niter page on mindat.org
• Niter page on webmineral.com
• Mineral galleries
• Poe's The Cask of Amontillado