ON THE CHEMICAL VARIABILITY OF PHOSPHATIC PARTICLES FROM JORDANIAN PHOSPHORITE DEPOSITS

The phosphate particles (pellets, intraclasts and skeletal fragments) from thirteen friable samples representing the economic phosphorite ho rizons in Jordan were hand-picked and then cleaned. A total of 39 part icle fractions were chemically analysed for their major and certain tr ace elements. The chemistry, supported by petrography, proved that the rounded particles are not faecal pellets; they are either rounded int raclasts or the rounded internal molds of bone cavities. The bone frag ments have higher contents of CO2, Na2O and SO3 and lower P2O5 and F c ompared with the pelletal/intraclast particles. These two groups of pa rticles are readily separated chemically. Since the environment of dep osition is the same, these differences are postulated to be due to the initial chemical composition of the bone material as carbonate hydrox yapatite (dahlite) and early diagenetic pathway conversion to carbonat e fluorapatite (francolite) versus the direct chemical precipitation, as francolite, of the pelletal/intraclast particles from the sediment pore water.