Ammonium nitrate is a natural mineral (ammonia niter—the ammonium analogue of saltpeter and other niter minerals such as sodium nitrate) found in the driest regions of the Atacama Desert in Chile. It is often a crust on the ground or found in conjunction with other nitrate, chlorate, iodate, and halide minerals. Although ammonium nitrate was mined in the Chilean desert in the past, nearly 100% of the chemical now used is synthetic. Ammonium nitrate does not readily burn, but accelerates the burning of combustible materials. However, it will burn if contaminated with combustible material. The colorless, odorless compound produces toxic oxides of nitrogen during combustion.
Ammonium nitrate is important as a fertilizer with an NPK rating of 34-0-0 (34% nitrogen). It is less concentrated than urea, which is rated at 46-0-0, giving ammonium nitrate a slight transportation disadvantage. Ammonium nitrate’s advantage over urea is that it is more stable and does not rapidly lose nitrogen to the atmosphere. During warm weather, urea is best applied soon before rain is expected or to cover it with soil to minimize nitrogen loss.
On its own, ammonium nitrate is not an explosive, but it readily forms explosive mixtures with varying properties when combined with primary explosives such as azides or with fuels such aluminum powder or fuel oil.