ABSTRACT

The fluorine content was determined spectrophotometrically for sedimentary rock samples from Tomioka, southern Gunma Prefecture. (1) Twenty six siltstones gave an average fluorine content of 420 ppm, and the value of each sample falls within a rather narrow range compared with that of chlorine. Chlorine in sedimentary rocks is quite labile against the attack of circulating water, whereas fluorine might not so easily be removed as chlorine. As a result, the fluorine content of sedimentary rocks is considered to be controlled mainly by the mineral species which constitute the sediments. (2) Tuffs which contain montmorillonite as a main constituent mineral tend to enrich more fluorine than those composed mainly of chnoptilolite.