The Fluorine, Chlorine, Bromine, and Iodine Contents of Volcanic Rocks in Japan

Abstract The halogen contents of 49 Japanese volcanic rocks are; F: 50–1700 (average 410), Cl: 17–1220 (av. 270), Br: 0.09–8.10 (av. 0.85), I: 0.011–0.32 (av. 0.088) μg/g. The fluorine and chlorine were determined by usual photometric methods, and the bromine and iodine, by photometric methods based on their catalytic action, after decomposition and separation procedures suitable for each case. The bromine and iodine contents are appreciably lower than the values generally accepted for igneous rocks. The bromine content agrees with Sugiura’s value. The frequency distribution of each halogen content shows an approximate lognormality. The chlorine and bromine contents are strongly correlated, and the Br/Cl atomic ratio is in a narrow range (0.66–3.7)×10−3 (av. 1.5×10−3). No other correlation is observed among the halogen contents at all. Each halogen content has no marked relation to the type of rock. A regional difference is seen in the F/Cl and I/Br ratios. Three ultrabasic rocks have very low fluorine (≤20) and chlorine contents (≤50 μg/g). On the other hand, they have a slightly lower bromine content (0.15–0.34 μg/g) than, and almost the same iodine content (0.07–0.13 μg/g) as, the volcanic rocks.