Investigation of fluorine distribution on the surface of acid-treated apatite single crystals using nuclear resonant reaction analysis

The surface of natural fluorine-containing apatite (fluoroapatite) single c rystals treated with acidic solutions of pH between 0.05 and 2.5 was invest igated by nuclear resonant reaction analysis (NRRA) techniques using the F- 19(p,alphay)O-16 nuclear reaction. The experimental results showed that par tial defluoridation takes place due to acid attack characteristically depen ding on the pH of the solutions. Powder-XRD data indicated that the crystal linity of the apatite surface was retained despite of the etch-pits observe d by SEM-EDS. Relevant investigations of the surface of acid-treated apophy llite crystals, a typical fluorine-containing mineral, indicated a complete amorphization and besides a total absence of fluorine.