It is found in impure form, often called saltpetre (also called nitre), its name derived from the Latin words sal patrae, meaning “salt of the rock,” as it is often found as a white material deposited on the surface of rocks. Saltpetre can form on the surface of soil in various warm-climate locations, including in Egypt, Spain, and Iran. In such places, feces, urine, and decaying plants react with moisture and an alkaline soil to create nitrates.