Phosphate Rocks Chapter 31: Ammonium Nitrate

Seven thousand miles south and west of Leith, the Atacama Desert sits on a plateau in the rain shadow of the Bolivian Southern Highlands, Peruvian Andes and Chilean Coastal Mountains. One of the driest places on earth, it is home to a huge deposit of sodium nitrate, once a valuable source of nitrates for fertiliser and explosives. 

A dispute over this valuable resource led to the 1879–1884 ‘Saltpetre War’ between Chile and a Bolivian–Peruvian alliance. 

Chile won. 

Now the desert is littered with abandoned mining towns – Chacabuco, Humberstone, Santa Laura, Puelma, and Oficina Anita – all shut down after the Haber-Bosch process for fixing nitrogen from the air led to the end of Chilean saltpetre exports. 

In Botswana, six thousand miles from Leith, and from Chile, bat droppings in Drotsky’s cavern have been transformed by bacteria over time into almost pure ammonium potassium nitrate. Named gwihabaite after the caves in which the mineral was found, these are the only known ‘natural’ sources of nitrates.