Abstract
Mineralogical properties of the green-colored material filling amygdales of the basalt at Kokuzô, Maruko-machi, Nagano Prefecture has been studied in detail. The chemical composition and X-ray powder data of the untreated sample resemble those of vermiculite. But, referring to other Xray data obtained after heating or treatment with ammonium nitrate or ethylene glycol, it has been revealed that the green material is a very complex mixture of clay minerals, namely, montmorillonite, vermiculite, random interstified combination of chlorite-vermiculite, and also regular interstratified combination of montmorillonte-vermiculite.
