Caliche at the Oficina Salitrera Humberstone. In Chile, nitrate salt deposits in the Atacama Desert are referred to as caliche. These deposits are the largest known natural source of nitrates in the world, containing up to 25% sodium nitrate and 3% potassium nitrate, as well as sodium iodate, sodium chloride, sodium sulfate, and borax. Caliche beds are mined and refined to produce a variety of products for agriculture or industry uses.