Aluminous phosphates of the crandallite series - a review

Abstract

Crandallite series minerals have general formula A AI3 (PO4) (PO(3)0H) (OH)6, where A are big cations like Na+, K+, Ca2+, Pb2+, Ba2+, Sr2+, ETR3+, and others with coordination 12, and several cationic and anionic substitutions may occur. They are often formed by weathering processes on different P-rich original materiaIs. Detritical deposits may also contain crandallite mineraIs, because of their high stability. They have been mentioned as the main source of phosphorus in soils. The recent increase in their recognition in marine sediments may modify former ideas about P quantities in this stage of its geochemical cycle. Crandallite phosphates, when associated with phosphatic ore,are generally considered harmful to mining and processing. lu Brazil, unlike other countries, they are not considered as raw material for phosphatic fertilizers. Their open structure, high stability, and relative abundance may represent enough arguments to find applications in different sectors. This paper presents a bibliographic review of mineralogical, geochemical and genetic aspects of the mineraIs of this series.