Refinement of the crystal structure of a vesuvianite [Ca_18.6 (Mn_0.3Fe_0.7) (OH)₂ (Mg_2.1Fe_0.7Ti_0.5Al_4.7) Al_4.2 (OH, O)₈ Si_18.2 O₆₈; a = 15.561(8) c = 11.777(7) Å; space group P4⁄nnc] from Nakatatsu mine, Fukui Prefecture, central Japan, was carried out by a least-squares method with X-ray single-crystal data. The final R index for 1901 observed independent reflections is 0.030. From site population refinement and observed interatomic distances of cation sites, the C-sites (square antiprism) and B-sites (tetragonal pyramid) are half occupied by Ca²⁺ and Fe²⁺ (+Mn²⁺), respectively, the A-sites (octahedron) are almost completely occupied by Al, and the AlFe-sites (octahedron) are occupied by Mn²⁺, Fe²⁺, Mg²⁺, Fe³⁺, Ti⁴⁺ and Al³⁺. From bond-valence calculations, the proton donor atoms are both O(10) and O(11). The cation site-populations and the hydroxyl groups of the structure models reported by ealier studies have been compared and reviewed.
Based on the structure analysis, the chemical formula of vesuvianite belonging to the space group P4⁄nnc should be written as Ca₁₉ (Mn, Fe²⁺) (F, OH)₂ (Mg, Fe²⁺, Mn, Al, Fe³⁺, Ti)₈Al₄ (OH, F, O)₈ (SiO₄)₁₀(Si₂O₇)₄.

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The crystal structure of masutomilite from Tanakamiyama, Ohtsu, Japan, has been refined by the X-ray single crystal method. The chemical formula is (K_1.79 Na_0.15 Rb_0.14)_2.08 (Li_2.54 Mn_0.99²⁺ Fe_0.18²⁺ Fe_0.06³⁺ Al_1.96 Ti_0.01)_5.74 (Si_6.65 Al_1.35)_8.00 O_19.64 (F_3.16 (OH)_1.20)_4.36 and the crystal data are as follows: monoclinic, C2, a = 5.262(2), b = 9.102(3), c = 10.094(3)Å, β = 100.83(2)°, Z = 1. The final R-value converged to 0.046 (wR = 0.052), using 519 independent reflections. The octahedral cation ordering, small Al and Fe³⁺ in the M(2) site, and the remaining large Li and Mn²⁺ in the M(1) and M(3) sites, results in the non-centrosymmetric C2 structure. The mean bond length of M(2)–O is 1.89Å, and those of M(1)–O and M(3)–O are 2.13 and 2.12Å, respectively.

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The high pressure crystal structure of phenacite Be₂SiO₄ has been studied based on single-crystal diffraction intensities collected at 22 kbar and 32 kbar. The result has revealed that the Be–O bonds show a large mean coefficient of linear compression 3.2×10⁻⁴ kbar⁻¹ ±1.3×10⁻⁴ kbar⁻¹ compared with the empirically predicted value 0.824×10⁻⁴ kbar⁻¹ for Be–O in general; the Si–O bond lengths are almost invariable in the pressure range covered.

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Crystal structure of Li₃N was studied by single crystal neutron diffraction using Time-of-Flight (TOF) method at a pulsed neutron source (KENS). Measurements were carried out at 400°C and at room temperature in wide range of wavelength and at a constant diffraction angle. After the refinements of anisotropic temperature factors using 32 reflection data at 400°C and 18 reflection data at room temperature, the thermal vibrations of atomic cores were shown. The directions of vibration coincide generally with the results of X-ray experiments.

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Fission track technique is most suitable for dating young obsidians due to their high uranium content (3–15 ppm). Lava flows from Lipari and Pantelleria islands in the Mediterranean basin have been dated. The hypothesis of historic origin of Lipari obsidians belonging to Rochhe Rosse and Forgia Vechhia flows is not confirmed and needs further investigations.

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