The chemical compound ammonium nitrate, the nitrate salt of ammonium, has the chemical formula NH4NO3, simplified to N2H4O3. It is a white crystalline solid which is highly soluble in water. It is predominantly used in agriculture as a high-nitrogen fertilizer. The compound is used as explosives in mining, and also sometimes in improvised explosive devices. It is the main component of ANFO, a popular explosive, which accounts for 80% explosives used in North America. It is used in instant cold packs, as hydrating the salt is an endothermic process.
Ammonium nitrate is found as a natural mineral (ammonia nitre—the ammonium analogue of saltpetre and other nitre minerals such as sodium nitrate) in the driest regions of the Atacama Desert in Chile, often as a crust on the ground and/or in conjunction with other nitrate, chlorate, iodate, and halide minerals. Ammonium nitrate was mined there in the past, but virtually 100% of the chemical now used is synthetic.