Some ferro-magnesian clay minerals occur in amygdales of pillow lavas from the Sunakobuchi formation (Miocene), western part of the Taiheizan, Akita Prefecture, Japan. A brown-coloured material (sample A) occurs in amygdales in the inner part of the pillow lava. This material is indentified as an iron-rich saponite by X-ray and chemical analyses. A dark green-coloured material (sample B) occurs in amygdales in the outer part of the pillow lava. Mineralogical properties of the sample B differ from those of the sample A. The visual inspection method of X-ray diffraction patterns before and after treatments clearly shows that the sample B is a randomly interstratified mineral of chlorite (0.45) and saponite (0.55). A small amount of celadonite also occurs sporadically in amygdales associated with the interstratified mineral.