Weathering Of Phosphate Minerals

Abstract

The known natural phosphate minerals exceed 250 in number (Fisher 1973). However, the more common ones are small in number and belong to the apatite family. This family constitutes the main group of primary phosphates of the lithosphere. The majority of the other minerals result from a supergene alteration by groundwaters, or bat- and bird-guanos. This alteration has been well described in detail by Altschuler (1973), in a fundamental synthesis based on three main topics: the weathering of marine phosphorites, the weathering of carbonatites and the weathering caused by acid guanos. The weathering of phosphatic igneous and metamorphic rocks is not mentioned, probably because it is little known, except in the northeast of Brazil (Lima Da Costa, verbal comm.). Since Altschuler’s synthesis, many studies have been published, some related to the weathering of phosphorites, others to the genesis of new minerals during the weathering process. Most of the mineralogical results obtained from these works are shown in Table 1. Consideration of Table 1 permits the findings of Altschuler (1973, p 78–80) to be extended and allows some general conclusions on the conditions of phosphate minerals weathering and on their behavior during weathering.