Nitrates usually occur as massive but delicate crusts on walls, roofs, and floors in caves, although some fine acicular crystals may also be found. These minerals are biogenic deposits. Nitrates were used as explosives, and several caves in Kentucky were mined for their saltpeter compound during the Civil War.
Crystal system: crystals rare, but may be found in hexagonal form. Color: colorless to white, gray, or reddish brown. Hardness: 1-2.
Soda niter is very soluble in water. Because it is so soluble, when taken out of a cave environment it may decompose (deliquesce) upon exposure to humidity in the atmosphere.
Color: white. Hardness: 2.
Niter, commonly called saltpeter, is a massive, encrusting mineral found on the surfaces and floors of caves. Like soda niter, niter is very soluble in water. Tufts of acicular crystals, similar to aragonite, may be found, and niter will not deliquesce.