抄録
Datolite of Somi is white in color and massive, occuring in the druses of metamorphosed rhyolite or dacite of the Miocene Sobosan volcanic rocks.
Optical data are: α=1.630, β=1.657_??_1.659, γ=1.667, 2V=(-)75. Chemical composition and X-ray powder data are shown in table 1 and 2.
It is associated with axinite, epidote, chlorite, grunerite-like amphibole, showing the mode of occurence different from any of the known cases such as limestone contact. Also, genetical problems of datolite from Japan are considered in this paper.
