The Boron Content of Volcanic Rocks in Japan

Abstract

The boron consent in about 130 Japanese volcanic rocks ranges from 0.5 to 169 μ g/g (Table 2), as determined by a spectrophotometric method based on the extraction of methylene bluetetrafluoroborate ion pair. The arithmetic mean (A. M.) is 21 μ g/g and the geometric mean (G. M.) is 14 μ g/g The cumulative frequency distribution of boron deviates distinctly from lognormality (Fig.1a). The alkaline rocks (or the rocks from the region near the Japan Sea)have low boron content (A. M.=6.2, G. M.=3.7) and con be clearly distinguished from the others by statistical analysis. On the other hand, glassy rocks have high boron content (A. M.=52, G. M.=36). The distribution of boron in these two classes of rocks and in the other rocks obeys lognormality, respectively (Fig.2). There is a slight tendency that the boron content increases with increasing silica content in rocks. The relation is, however, not so clear as has been usually refered. The boron content has also no marked relationst to the eontents of other volatile components such as fluorine or chlorine. The distribution of the B/Cl ratio shows lognormality(Fig.3), but that of the B/F ratio shows two separate lognormal distributions. Each of them correspends to the rocks from the Japan Sea region (or the alkaline rocks) and the others (Fig.4).Ultrabasic rocks analyzed have low boron contents as compared with volcanic rocks (Table 3). The boron content of usual rock forming minerals were found to be almost the same as that of volcanic rocks. Almost all of them were, however, water-soluble and can not be regarded as contained in their crystal structures (Table 5).