Studies on the Sulphur and Iron-Sulphides Deposits of the Matsuo Mine (3)

On the Saponitized Andesite

Abstract

A green mineral, found in the greenish altered andesite underlying the Matsuo sulphur deposits, was studied by means of microscope, differential thermal and X-ray analyses. From the results of these studies, it is concluded that the green mineral consists mainly of iron-saponite associated with some kaolin mineral.
The iron-saponite occurs in green aggregates of fibrous, lamellar and irregular crystals, replacing phenocrystic pyroxene, plagioclase and a part of the groundmass where it is associated with cristobalite and a carbonate mineral. Thus the andesite should be called a saponitized andesite.
It seems to have been formed by the action of residual solutions, neutral or very weakly alkaline in nature, which reached there throughout a zone of montmorillonitic alteration.