50.—Nitre.
Occurs in thin crusts, delicate needles, or disseminated through the loose earth in caves; glossy lustre; brittle; cool, saline taste; crackles and burns brightly on live coals; a little harder than Gypsum.
Value.—Used in the manufacture of gunpowder, fulminating powders, nitric acid, etc.
Localities.—Marion County, Ky.; White County, Tenn.; near Rosiclare, Ill.; Silver Peak, Nev.