Published online by Cambridge University Press: 14 March 2018
(1) Long spacings (29·6 and 26·7Å) are confirmed from certain clays from Japan. (2) These clays have very complicated clay mineral compositions including kaolin minerals, chlorite, sepiolite and montmorillonite. (3) Each long spacing can be explained by a regular interstratification between two kinds of lattices selected from the following ones: montmorillonite (cell ht. 15·4Å), a magnesian chlorite (14·5Å), sepiolite (12·7Å), and a new lattice (14·0Å); the last is a regular interstratitication of gibbsite and silicate (pyrophyllite unit) layers. The new lattice is proposed not only to explain the spacing but all other mineralogical properties of the clay. Thus the 29·6Å spacing agrees well with that of a 15·4/14·0Å super-lattice, and the 26·7 Å spacing with a 12·7/14·5Å super-lattice. (4) These long spacings are liable to be found in a clay in which several kinds of clay minerals co-exist, and such a complex clay tends to be found in special conditions, such as a boundary area between two different kinds of alteration zones, and/or an area affected by successive hydrothermal alteration.