Abstract
Samples of brushite, hydroxylapatite, and taranakite collected from seven karst caves of Apulia (southern Italy) have been investigated by means of chemical analysis and by DTA and XRD techniques. Brushite is found to crystallize in very pure form, whereas hydroxylapatite and taranakite show several isomorphous substitutions. A high Zn content was detected in hydroxylapatite. The TG curves for one sample of hydroxylapatite show a weight loss greater than the total H2O content, probably because of the loss of S. DTA and XRD analyses of taranakite indicate that the formation of AlPO4 at 1200 °C is not a reversible reaction.
In accord with previously published paragenetic sequences, the minerals were probably formed by interaction between phosphatic solutions derived from bat guano and the substratum minerals, specifically calcite and clay minerals. However, the data also suggest precipitation from solution for brushite and hydroxylapatite.
