FLUORINE EXCITATION DURING APATITE ANALYSIS

Data were obtained in 6 s counting intervals separated by 3 s of beam blanking. Background was determined by separate measurement at wavelengths above and below the peak on immediately adjacent spots. 

Stormer et al. (1993) also conclude that apatite Cl X-rays respond similarly. The initial Cl X-ray intensity increase takes place on a similar time scale (Stormer et al. 1993). However, Cl X-rays are not absorbed as strongly as F X-rays in the apatite matrix, so as the Cl X-rays are brought surfaceward, their emergent intensity is not significantly increased. 

A survey of several analyses of apatite from the geological literature demonstrates that the increase in apatite F X-ray intensity was unrecognized, or ignored. Stoichiometric Ca-fluorapatite contains 3.76 wt % F, but several analyses from the literature (Amli 1975, Bea and Montero 1999, Kifer and Wolf 2000) report apatite F contents well in excess of 4 wt %, with extreme values approaching 6.5 wt % (Bea and Montero 1999). When normalized to a +25 total cationic charge, apatite analyses such as these yield F atom totals far in excess of 1.0, indicating major problems with the apatite analytical routines used in these studies. 

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