The Chemistry of World Calcrete Deposits

Abstract

Over 300 published and unpublished analyses of calcrete (caliche), together with additional data generated by the author, have been processed to obtain an indication of the nature of world calcrete chemistry and the variability between major regions. Calcium carbonate, in the calcitic form, is the dominant constituent (over 79%), silica is second in importance, with its concentration varying inversely with that of the calcium carbonate, and magnesium carbonate is only exceptionally quantitatively important. Ses-quioxides, manganese, gypsum, and phosphates are locally important. The insoluble residue consists of aeolian sand grains in tropical deserts, silt and clay, particularly in subtropical examples, and amorphous silica in the form of opal, or chalcedony. Palygorskite (attapulgite) is often a major clay mineral. The data enable comparisons with recent analyses of American caliches, and particular reference is made to samples from the Kalahari of southern Africa, Libya, Cyprus, Kenya, and South-West Af...