The crystal structure and cation distribution of a 2M₂ lepidolite coexisting with the 1M form, from Rozna, Moravia, Czechoslovakia has been determined by least squares refinement employing three-dimensional intensity data collected by the precession method with MoKα radiation. The tetrahedral rotation angle, α, is 5°, thus making the inner oxygen coordination around potassium into trigonal prism. Determined site occupancies and bond lengths show that most of the aluminum is concentrated into position 8ƒ(M2 site), as was observed in polylithionite by Takeda and Burnham.
Structural changes that accompany polymorphic transitions from 1M or 2M₂ lepidolite to 2M₁ muscovite, are discussed in terms of the bond lengths, tetrahedral rotation angle, tetrahedral collapses, OH-F substitution, K-F configuration, and Madelung sums.

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Polytypes of silicon carbide with long c-periodicity and stacking disorder have been studied by the X-ray single crystal method and phase-contrast microscopy. It has been found that all the long-period polytypes treated in this investigation have spiral growth patterns on the (001) face, with step heights corresponding to the X-ray unit cell dimensions. It has also been confirmed that the specimens containing a long-period polytype consist of syntactic coalescence of two or more polytypic structures and that the disordered type with stacking faults along the c-axis always intervenes at the contact region of the long-period polytype with the fundamental one. On the basis of these observations, the formation mechanism of long-period polytypes is discussed, and the crystal structure of 81H, which is one of the long-period polytypes discovered during the investigation, was determined to have the Zhdanov notation (33)₅35(33)₆34.

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Thermal transformation of SiC crystals were studied experimentally. Needle-like 2H crystals prepared by the gaseous cracking method were heated up to 1, 200-2, 300°C, and when brought down to room temperature, their X-ray oscillation photographs were taken. Diffuse streaks appeared along the c^*-direction in the diffraction pattern of the specimen heated at 1, 600°C, and then spots due to 3C emerged along the streaks. At 1, 900°C, spots due to 4H appeared and at 2, 000°C those due to 6H. The spots from 3C disappeared at 2, 100°C. Throughout these changes, the external form of the specimen remained unchanged and most part of 2H persisted. At 2, 300°C, only spots observed were those from 2H and 6H. From these findings, it was concluded that 3C, 4H, 6H and probably 2H are thermodynamically stable phases, and their relative amounts were estimated at each temperature. The mechanism of the transformations was believed to be due to the periodic slip process, and stacking disorder was confirmed to be the sole phenomenon premonitory of the transformations and capable of lowering the extremely high potential barriers attached to these transformations.

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Magnetite in dacite from Haruna Volcano, Central Japan has been studied in detail with the electron probe microanalyser. It is found that the magnetite shows a distinct compositional variation before and after the eruption of magma; ΣFeO, Al₂O₃ and MgO decreased, while TiO₂, V₂O₃ and MnO increased. Magnetite inclusions in the other crystallizing phases also show the same compositional change. By correlating the chemical compositions of discrete magnetites with those of the inclusion magnetites, the relative stage of crystallization of the minerals enclosing the magnetite inclusion can be estimated.

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Coexisting inverted protoenstatite and bronzite from Cape Vogel, Papua (Dalwitz, Green & Thompson, 1966) were re-examined to obtain partition coefficient of Mg and Fe between contiguous protopyroxene and orthopyroxene. Stability relations of pyroxenes in the system MgSiO₃-FeSiO₃ are suggested mainly on the basis of the partition coefficients of Mg and Fe between natural coexisting protopyroxene and orthopyroxene and between natural coexisting orthopyroxene and Ca-poor clinopyroxene. The most probable isothermal sections in the Mg-rich part of the ternary system CaSiO₃-MgSiO₃-FeSiO₃ are presented.

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