Complete solid solubility was confirmed in the pseudobinary system Ba₂TiGe₂O₈–Ba₂TiSi₂O₈ and phase boundary between orthorhombic and tetragonal phases was determined by DTA and polarizing microscopy. At room temperature, the phase boundary is passing through about 45 at% Si for the tetrahedral cations. The crystal structures of Ba₂Ti(Ge_0.25Si_0.75)₂O₈ and the paraelastic Ba₂TiGe₂O₈ were determined from single crystal X-ray diffraction data. The space groups, cell dimensions and final R values are: P4bm, a=8.583 (1), c=5.268 (1) Å and 0.039 (440 reflexions at room temperature) for the former crystal, and P4bm, a=8.770 (1), c=5.433 (1) Å and 0.076 (182 reflexions at 890°C) for the latter. The structures of both crystals consist of (Ge, Si)₂O₇ groups and TiO₅ square pyramids to form flat sheets perpendicular to the c-axis. Paraelastic Ba₂TiGe₂O₈ has highly distorted GeO₄ tetrahedra. Average (Ge, Si)–O distances are 1.73 and 1.65Å and bridging angles O–(Ge, Si)–O are 131° and 137.4° in the paraelastic Ba₂TiGe₂O₈ and Ba₂Ti(Ge_0.25Si_0.75)₂O₈, respectively.

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Growth and dissolution rates of {100} faces of NaClO₃ crystals of about 0.5 mm across have been measured, along with in-situ observations of both processes, under a wide range of well-controlled super- and under-saturations, 1.1∼49%, and 1.6∼4.5%, respectively. The experiments were made using a specially designed apparatus, with which both growth and dissolution experiments can be made on the same seed crystal. The growth mechanisms are analysed based on the relation between the bulk supersaturation σ_B and the growth rate R. Physical constants, such as γ′⁄kT, etc. were evaluated.
It is concluded that in the lower supersaturation range than σ_B≈2.5% BCF mechanism predominates, in moderate supersaturation range 2.5<σ_B<8.0%, Birth and Spread mechanism of two dimensional nucleation growth is the major growth mechanism, and in much higher supersaturation range, 8.0%>σ_B, maximum linear law is assumed to be operated. Dissolution mechanism is also briefly discussed, in which the importance of interface kinetics is stressed. The observations on the recovery process from rounded to facetted morphologies and on the occlusion of liquid inclusions are described as well.

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Mineralogical properties of tobelite, a new ammonium-dominant dioctahedral mica, found in the Ohgidani pottery stone deposit at Tobe, Ehime Prefecture, Japan, are described.
This mineral, accompanied by quartz, occurs as a hydrothermal alteration product of a biotite andesite dyke. Wet chemical analysis gives a structural formula: ((NH₄)_0.53K_0.19Na_{0.01    0.27})_1.00 (Al_1.97Ti_0.00Fe³⁺_0.03Mg_0.05)_2.05(Si_3.17Al_0.83)_4.00O₁₀(OH)₂. The low interlayer charge is explained with its poorly crystallized nature. The X-ray powder diffraction pattern is very close to that of synthetic NH₄Al₂Si₃AlO₁₀(OH)₂ by Eugster and Munoz (1966), and is satisfactorily indexed on 1M polytype cell having a=5.219Å, b=8.986Å, c=10.447Å and β=101.31°. Space group may be C2⁄m. Tobelite is characterized by its larger unit layer thickness (10.25Å) than that of potassium dioctahedral mica. This material yields an endothermic reaction and absorption bands specific to ammonium in DTA curve and infrared spectrum, respectively. Optically it is biaxial, negative, 2V_calc.=28°. Refractive indices are α=1.555, β=1.575, γ=1.581, all±0.002.
Mineralogical description is made also on tobelite from the Horo pyrophyllite deposit, Hiroshima Prefecture, Japan, which is well crystallized as compared with the Tobe material and is tentatively determined to be of 2M₂ polytype.

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