What is saltpeter? Saltpeter, also known as niter is potassium nitrate (KNO3). It is a mineral classified with the carbonates. Its properties are therefore similar to those of limestone.

When and how was it deposited? It is formed in warm climates by bacterial action during the decomposition of excreta and vegetable matter. In Tennessee it is generally formed in caves from bat droppings, called guano. The contact between the rotting material and limestone allows 'nitrification' - that is the conversion of nitrogen compounds from animal and plant decay into nitrates which penetrate the soil. Dissolved in rainwater, the deposits evaporate on the surface to form a white powder, which is a crude saltpeter. (paraphrased from "SALT...made the world go round")

What is saltpeter used for?

Saltpeter is used for two entirely different purposes: (1) It is used as a fertilizer. Plants need nitrogen, but cannot use nitrogen directly from the atmosphere. Nitrates are one form which plants can use; (2) Saltpeter is one of the three ingredients in gunpowder.

The two faces of nitrates was demonstrated in 1995 when Timothy McVeigh went to a farm supply store and bought the closely related fertilizer ammonium nitrate and used it to blow up the Murrah Federal building in Oklahoma City.

After the Civil War, cheap saltpeter made from bird guano in Chile became available and demand for domestic saltpeter dropped.

During the First World War (about 1918) scientists developed methods for producing nitrates in the laboratory, further reducing the demand for natural saltpeter.

Environmental consequences of saltpeter mining. In the 19th century, people did not appreciate what fragile environments caves are. We now understand that the dissolving, percolating, and recrystallizing of soluble minerals is the essential process of cave formation.