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 horizons in Jordan were hand-picked and then cleaned. A total of 39 particle fractions were chemically analysed for their major and certain trace elements. The chemistry, supported by petrography, proved that the rounded particles are not faecal pellets; they are either rounded intraclasts or the rounded internal molds of bone cavities. The bone fragments have higher contents of CO2, Na2O and SO3 and lower P2O5 and F compared with the pelletal/intraclast particles. These two groups of particles are readily separated chemically. Since the environment of deposition is the same, these differences are postulated to be due to the initial chemical composition of the bone material as carbonate hydroxyapatite (dahlite) and early diagenetic pathway conversion to carbonate fluorapatite (francolite) versus the direct chemical precipitation, as francolite, of the pelletal/intraclast particles from the sediment pore water.