抄録
Smectite and various interstratified chlorite/smectite (C/S) are widely distributed in the Miocene basic volcaniclastic sediments of the Green Tuff Formation (Aosawa basalts) in the Dewa Hill, Yamagata Prefecture. These clay minerals have been investigated by X-ray, chemical and thermal analyses as well as microscopic observation.
Transformation process from smectite to interstratified C/S is explained as follows. At first, Mg-rich smectite had been deposited from pore solution which contains dissolved substances as a result of reaction of interstitial seawater with basaltic glass. In the second stage, by increasing temperature, the smectite had transformed to randomly interstratified C/S (chlorite layer<33%), that is fine-grained and low interference colored crystal. Finally, regularly interstratified C/S (corrensite) had been produced by recrystallization.
Transition from smectite to corrensite in the Aosawa basalts is not continuous: it is characterized by discontinuous stepwise change between C/S (chlorite layer<33%) and corrensite (chlorite layer 40-50%).
