Abstract
The optical angles (2E) and base-exchange capacities of vermiculites which occur in weathered granodiorite near Ono-machi, Fukushima Prefecture, were measured. The optical angles of these vermiculites vary in values, showing the maximum 27° or less, and generally small angle in altered specimens. It was shown that the mean value of the base exchange capacities of these vermiculites were about 1.80m. e. per gram, and these specimens were Ca-vermiculties containing exchangeable Ca ions.
The X-ray powder patterns and refractive indices of the specimens which were exchanged by H, Na, Ca, Mg, Ba, were compared. It was shown that the refractive indices of these specimens gave very high values in general (γ=1.66_??_1.677). Generally, the refractive indices of the specimens which have large optical angles, are considerably high and Ba-exchanged specimen shows the highest index among Na-, Mg-, H-, Ca-, Ba-, exchangd ones. It was assumed that the pegmatitic residue affected the formation of the vermiculite of this area.
