Spiral steps observed on hematite crystals from Sasazawa, Nagano Prefecture, Japan show undulation of varying degrees depending on their heights and on the faces. Laboratorical etching produced etch hillocks, instead of etch pits, along the steps, corresponding to the undulation. At the summits of etch hillocks, crystallites of Mn–Ti rich phase were observed. From these, it was concluded that the observed step undulation was due to the precipitation of these crystallites, which played a role of obstacles against the advancement of spiral steps, and of heterogeneous two-dimensional nucleation site. The crystallites precipitated epitaxially on the {0001} surface, whereas they adhered selectively along the steps on the {10-11}. On the {11-20} surfaces, they selectively precipitated along the cliff created by twinning, and played a role of heterogeneous two-dimensional nucleation sites.

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The phase chemistry and the structure of hollandite-cryptomelane series in the Precambrian Sausar Group of India are reinvestigated. The tunnel-cations of the hollandite-cryptomelane series of the present investigation do not show complete exchanges. Crystal symmetry of these minerals is affected by the amounts and the composition of the tunnel cations. With increasing Ba²⁺ content, symmetry of cryptomelane in Tirodi area changes from tetragonal to monoclinic. These minerals appear to have been formed in a wide range of metamorphic grade from the lowest (chlorite-biotite) to the highest (sillimanite) grades. The local breakdown of hollandite to hausmannite ±Ba-feldspar must have occurred by the change of f_O2 condition of the system during metamorphism.

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Aluminosilicate glasses containing H₂O (NaAlSi₃O₈·1.88H₂O, Na_0.57Al_0.57Si_3.43O₈·1.69H₂O, Ca_0.38Al_0.77Si_3.23O₈·1.71H₂O) were synthesized by the hydrothermal method, and their structures were studied by the X-ray diffraction method. All of these glasses have TO₄ (T = Si, Al) tetrahedra as basic structure units like in anhydrous aluminosilicate glasses. However, shapes of correlation functions are different from those of the corresponding anhydrous ones in the longer range than 3.5Å. Main structural changes induced by the addition of H₂O are breakdown of linkage of TO₄ tetrahedra to form clusters.

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The formation of extracellular crystal aggregates of bobierrite (Mg₃(PO₄)₂·8H₂O) by Acinetobacter sp. is found with the use of B-17 medium. The crystal aggregates were observed in the colonies as deposits of brown-yellow coloration, and were identified by X-ray powder diffraction, chemical analysis, infrared spectra and scanning electron microscopy. The production of bobierrite by soil bacteria may imply further versatility of the crystals formation by microorganisms.

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Single-crystal X-ray diffraction experiments were carried out on NiS₂ under high pressures with the aid of a diamond-anvil cell. The pressure dependence of the a dimension was found to be linear over the experimental pressure range across the transition point with a good approximation. The S–S bond length is practically constant up to the transition pressure and decreases rapidly above it. The Ni–S length decreases with pressure both in the semiconductor and metallic phases within the pressure range of this experiment. However, the decrement is slower in the higher pressure, metallic phase than in the semiconductor phase. Discontinuities in the plots of bond lengths against pressure are not so large as can be recognized with the precision of this experiment.

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The crystal structure analyses of stishovite were carried out by X-rays using a single crystal under pressure up to 6.09 GPa. The linear compressibilities β_a = 1.22×10⁻³ and β_c = 0.64×10⁻³ GPa⁻¹ and the isothermal bulk modulus of K_T = 313 GPa were obtained from the lattice parameters. A shared-edge is the shortest of three kinds of oxygen edges in SiO₆ octahedron and is of highest compressibility, resulting in an enhancement of distortion of the octahedron with increasing pressure. The bulk modulus of SiO₆ octahedron is evaluated to be 250 GPa which is smaller than that of the tetragonal unit cell. Shortening of the shared-edge of SiO₆ octahedron with pressure can be explained by shielding effect for increasing cation-cation interaction along the c-axis and may suggest an increasing tendency of covalent character of stishovite with pressure.

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