Geochemistry of Egyptian Francolites PDF

Keywords

cation, anions, francolites

Abstract

The Cretaceous Duwi (phosphate) Formation of the Nile Valley (Mahamid area) and Red Sea (Nasser, Yunis, Queih and Um el Heutat areas) were studied. Ca, P, F, Na and Mg were determined quantitatively using the electron microprobe analyzer. Francolite is the principal phosphate mineral in the studied samples. It exhibits different isomorphous substitutions. Red Sea francolites show relatively high cation substitutions. About 5% of the Ca ions can be replaced by Na and Mg. Maximum cation substitutions should take the form Ca(9.54) Mg(0.10) Na(0.36). The Nile valley francolites show relatively high anion substitutions. About 10% of the (PO4) group is replaced by the (CO3) group and/or (CO3 + F) group. Maximum anion substitutions should take the form Ca(9.54) Mg(0.10) Na(0.36). The Nile valley francolites show relatively high anion substitutions. About 10% of the (PO4) group is replaced by the (CO3) group and/or (CO3 + F) group. Maximum anion substitutions should take the form (PO4)5.39 (CO3F)0.61. Such variable substitutions are attributable to the effect of formational and secondary alteration environmental