GEOLOGICAL OCCURRENCE
Phosphate rock is a sedimentary deposit containing phosphate of lime. It occurs as a hard rock interstratified with beds of sandstone, shale, or other sediments; as amorphous nodular concretions or pebbles in stream deposits; and as a residuum from the decomposition of phosphatic dolomite or limestone, or other rocks containing phosphate of lime. Another type of deposit commonly classed as phosphate rock is the porous coralline or other limestone of tropical islands which has been permeated with phosphate leached from guano.
Phosphate deposits of the western United States, Algeria, Tunis, and Egypt are hard rock beds of the first type. Amorphous nodular deposits occur in South Carolina, part of Florida, Wales, England, Belgium, north-central and eastern France, and Russia. The deposits in Tennessee, Kentucky, and some of those in Florida are residual. Leached guano deposits are found on the islands of Aruba, Curacao, and Sombrero, in the West Indies, and on Christmas, Ocean, Makatea, Angaur and other islands in the Indian and South Pacific oceans.
The reserves in the United States are fairly well known and are estimated at 6,000,000,000 tons. Reserves of high-grade rock in Algeria and Tunis have been estimated at 300,000,000 tons. No information is at hand regarding the quantity of phosphate rock in Egypt or in Europe, except that Russia is believed to have 80,000,000 tons in one of its fields. The deposits in the South Pacific islands are estimated at 70,000,000 tons. Before the war the world’s output of phosphate rock was about 6,000,000 tons annually, of which about one-half was mined in the United States. The next largest production is made in northern Africa.
Phosphoric acid is derived also from apatite, a calcium phosphate that occurs in veins. Apatite has been mined in the Province of Quebec, Canada, and in Spain.