Chemistry of Kornerupine and Associated Minerals, a Wet Chemical, Ion Microprobe, and X-Ray Study Emphasizing Li, Be, B and F Contents

Kornerupine and associated minerals in 31 samples of high-grade rocks relatively rich in Al and Mg were analysed by wet chemistry, ion microprobe mass analyser, electron microprobe and X-ray powder diffraction. For 11 samples of kornerupine and three samples of biotite (F only) analysed by both wet chemical and ion microprobe methods, the best agreement was obtained for B2O3, whereas the ion microprobe Li2O values were systematically somewhat higher than the wet chemical values. The wet chemical methods give Li2O=0–0·19 wt.%; BeO=0–0·032 wt.%; B2O3=0–4·01 wt.%; and F=0·07–0·77 wt.% in kornerupine, whereas ion microprobe analyses on other kornerupines give values up to 0·35 wt.% Li2O, O066 wt.% BeO, and 4·72 wt.% B2O3. The sum B+Al+Fe3++Cr is close to 6·9 atoms per 22 (O, OH, F) or 21·5 (O) in kornerupine. In general, Li/Fe ratios decrease as follows: kornerupine »sapphirine≥biotite > Crd (Na<0·03 per 18 oxygens)>tourmaline, garnet, orthopyroxene. However, for cordierite with Na>004, Li/Fe decreases as follows: cordierite>kornerupine. Sapphirine and sillimanite are the only associated minerals to incorporate significant boron (0·1–0·85 wt.% B2O3) and then only when the single site for B in kornerupine is approaching capacity. Sillimanite B2O3 contents increase regularly with kornerupine F. Fractionation of fluorine increases as follows: kornerupine<biotite