Abstract
The chemical composition (up to 7 elements) of francolite in 64 samples of Israeli phosphorites from 7 fields was determined. Samples comprising mainly skeletal macrograins contain, on the average, 1.5% less P2O5, than those with other types of macrograins (mostly pelletal). Average CO2 in the skeletal variety is 4%, against 3% elsewhere. There is a strong positive correlation between Na and CO2, and a strong negative one between Mg and P2O5. Of the principal components explaining more than 95% of the chemical variation, the first, which opposes phosphate to carbonate and to sodium, differentiates between types of macrograins; the second, based on calcium and sodium not coupled with carbonate, differentiates between phosphorite fields. This is clearly seen from the graph (Fig. 6) obtained by correspondence-factor analysis. The difference between skeletal and other magrograins could be due to origin or to diagenetic changes, which include “francolitisation” of carbonate hydroxyapatite.
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