A titaniferous oxyhornblende from Korea was found to be built up on two different lattices, one being the monoclinic amphibole lattice (I2/m), the other the monoclinic pyroxene lattice (C2/c). The two minerals, the proportion of which varies from specimen to specimen, are presumably grown submicroscopically side by side.

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Stevensite, a magnesium end member of trioctahedral montmorillonites, contains a variable amount of interlayer water molecules. The elimination of these interlayer water molecules on heating accompanied with some kinds of structural changes was traced in the experiments with a high temperature X-ray diffractometer and a thermobalance. Dehydrated stevensite generally has an interstratified structure composed of two or three of the fundamental layers having thicknesses of 15.4 A, 12.5 A, 9.7 A and 9.5 A. The 15.4 A later has double sheets of hexagonally arranged water molecules in each interlayer position, and each water sheet is composed of about five water molecules per unit mesh of the ab plane (a=5.2 A and b=9.1 A). The 12.5 A layer has a single water sheet, equivalent to one of the components in the double sheets of the 15.4 A layer, in each interlayer position. The 9.7 A layer has a structure similar to that of mica, and has a sheet of two water molecules per above-mentioned mesh in each interlayer position. The 9.5 A layer has a talc-like structure and does not contain interlayer water. During dehydration several kinds of regular structures appear. They are as follows in the order of decreasing hydration degree: 15.4 A type, composed only of 15.4 A layers;
25.0 A type, having regular sequence of 15.4-9.7A layers;
22.0 A type, having regular sequence of 12.5 A-9.7 A layers;
84.0 A type, having perhaps regular sequence of 12.5 A-9.7 A-9.7 A-9.7 A-9.7 A-9.7 A-12.5 A-9.7 A layers;
9.7 A type, composed only of 9.7 A layers;
19.2 A type, having regular sequence of 9.7 A-9.5 A layers; and
9.5 A type, composed only of 9.5 A layers.
Random interstratifications occur between two adjacent regular structures.
Beyond the formation of the structure of the 9.5A type, the layer structure is unstable, and it finally breaks down into enstatite and silica.
From the knowledge of structures and modes of interstratifications, dehydration mechanism of stevensite, reversible and irreversible, is also discussed.
hand, the structures of the irreversible dehydration stage have no 5-H₂O sheet and thus potential bonds which are strong enough to attract other 5-H₂O sheets can not be expected.
Though many problems remain still unproved, it can be concluded that the dehydration of stevensite in the interlayer positions is quite continuous and that the phenomenon is explained by the continuous change of modes of interstratifications which occur among fundamental layers of several kinds. Such interstratifications take place with some regularities by eliminating the interlayer water sheets and by changing the types of the interlayer water sheets, and become regular in some cases and random in the other.

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Tridymite was synthesized under various conditions with respect to starting materials and mineralizers in room pressures. Some of them, in its X-ray powder diffraction data, show the features of tridymite M and tridymite S, which were confirmed by Hill and Roy in sythetic tridymite under the hydrothermal condition, and the others are grouped into the intermediate between M and S. As the rusults of examination of their X-ray powder reflections and their D. T. A. curves, detailed criteria for grouping the tridymites by X-ray means in the present experiments were given along with the suggestions that these differences are due to the distortion of the structure at high-low inversion.

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Lattice constants and space group of low tridymite of type M dtermined here are: orthorhombic; a=9.940A, b=17.21A, c=40.92A; space group C222₁. The long period in the c-direction is caused by minor transverse displacements of constituent atoms along (0 0.1), which simulatneously form the double period in the a-direction, both associated with the phase transition of tridymite.

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