The microstructure of hydrobiotite, interstratified biotite/vermiculite, was examined to demonstrate an atomic scale investigation of weathering of minerals by high-resolution transmission electron microscopy (HRTEM). Vermiculite basal spacing was collapsed to about 0.95 nm, compared to the unchanged biotite 1.0 nm spacing, by dehydration probably during the ion-milling sample preparation. Atom-resolving structure images with 0.2 nm point resolution show a distinct difference between K-containing and K-depleted interlayers, corresponding to biotite and vermiculite respectively. Thus, the difference in image enables us to identify vermiculite layer positions in hydrobiotite unambiguously. Although the vermiculite layers are randomly formed in the original biotite, there is a tendency to form 1:1 regular biotite/vermiculite interstratification locally. In some interlayers the contrast of potassium columns changed gradually, which suggests that biotite is directly transformed to vermiculite in the weathering process. These observations demonstrate atom-resolving HRTEM is a useful method for structure analyses of such water containing secondary minerals as vermiculite in spite of spacing changes caused during sample preparation or observation in TEM.

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Calorimetric study was performed to measure relative enthalpies of alkali tetrasilicate glasses quenched from melts at various pressures. The high-pressure K₂Si₄O₉ and Na₂Si₄O₉ glasses were obtained by quenching the melts at about 2273–2473 K in the pressure range from 3 to 12 GPa. The enthalpies of the glasses were measured by a differential drop-solution calorimetry method in 2PbO·B₂O₃ solvent, using a Calvet-type microcalorimeter. Densities of the glasses were also measured by the Archimedes method. Relative enthalpies and densities in the K₂Si₄O₉ and Na₂Si₄O₉ glasses increase with increasing the synthesis pressure. Compared with those of the 1 atm-glass, relative enthalpy and density of the K₂Si₄O₉ glass synthesized at 8 GPa are higher by 28.1 kJ/mol and 11.0 %, respectively, and those of Na₂Si₄O₉ glass higher by 33.1 kJ/mol and 25.1 %, respectively. These large enthalpy increases are consistent with pressure-induced structural changes in K₂Si₄O₉ and Na₂Si₄O₉ glasses in which the proportion of five- and six-coordinated Si increases with pressure: total abundance of the high-coordinated Si increases up to about 12 % in all of Si in the Na₂Si₄O₉ glass synthesied at 12 GPa and about 5 % in the K₂Si₄O₉ glass at 5.5 GPa. In contrast to these large enthalpy changes in the alkali tetrasilicates, enthalpy increase in NaAlSi₃O₈ glasses quenched from melt at 1.5–2.5 GPa was only 2–3 kJ/mol, because only a small structural change in the medium range (decrease of mean T-O-T angles) occured in this pressure range.

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The thirteen microprobe analyses of ferrierite from Monbetsu are differentiated into two groups due to Na₂O contents. The averages of ten Na2O-free and three Na₂O-bearing analyses are, respectively, SiO₂ 65.78, 66.87; Al₂O₃ 12.89, 12.86; Fe₂O₃–, 0.16; MgO 3.32, 3.30; CaO 1.35, 1.26; BaO 0.78, 0.78; Na₂O–, 0.47; K₂O 0.86, 0.86 wt.%. The absence of intermediate analysis presents an example of compositional variation of ferrierite in a single specimen, although the difference is approximately given as the simple addition of Na₂O contents and the concomitant increase of SiO₂ content to the latter. The H₂O content measured by Karl Fischer method is 14.29 wt. %, giving totals 99.27 and 100.85 wt. %, respectively. Their empirical formulae (basis: total O = 72 in the anhydrous part) are, K_0.49(Ca_0.65Ba_0.14)_Σ0.79Mg_2.21Al_6.77Si_29.31O₇₂·21.23H₂O and (K_0.48Na_0.40)_Σ0.88(Ca_0.59Ba_0.13)_Σ0.72Mg_2.16(Al_6.65Fe_0.05)_Σ6.70Si_29.31O₇₂·20.89H₂O, respectively. The X-ray powder pattern is indexed on a body-centered orthorhombic cell with a=19.239, b=14.142, c=7.513 Å. The relationships a vs Si and a vs Mg contents agree with the existing data. It occurs as minute blades elongated to c-axis and flattened to a-axis grown on pyrite and magnesian siderite perpendicular to the walls of open fractures in an altered baslt intrusive, in which closed fractures with smectite and pyrite without ferrierite had been formed prior to open fractures. Wider ferrierite-bearing open fractures include tabular calcite, which forms independent veinlets in the quarry, this being more common therein. The basalt body belongs to a member of Miocene Kohnomai Formation, in which many hydrothermal gold-silver veins of the Kohnomai mine were formed, and the ferrierite locality is included within th area of metallic mineralization. The geneses of ferrierite and the direct associates are considered. Pyrite and magnesian siderite are the reaction products of incorporated H₂S and CO₂ with a solution containing Mg²⁺ and Fe²⁺ derived from the alteration of mafic minerals in the basalt by ascending hydrothermal solution. Ferrierite is located between siderite and calcite in sequence of formation, alkaline or neutral condition being needed, besides residual Mg and high silica nature of the solution.

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The chemical composition of romeite from the regionally metamorphosed bedded manganese ore deposit of the Gozaisho mine, Fukushima Prefecture, is (Na_1.00Ca_0.80Mn_0.01)_Σ1.81Sb₂ [O_5.69F_0.89(OH)_0.36]_Σ6.94, calculated on the basis of Sb=2. It occurs as honey yellow to brownish yellow octahedra up to 4 mm long in braunite-rhodonite ore. It is cubic, Fd3m, a=10.265(2) Å, Z=8. Microbalance measured specific gravity is close to the calculated density 5.096 g/cm³. The single crystal study using the four-circle diffractometer confirms the isostructural relation to pyrochlore and stibiconite group minerals, yielding R=1.3%; Rw=1.8%. The precise ideal formula of romeite is to be simply NaCaSb₂O₆(F, OH). The quantitative relation of Na to Ca is similar to the case of pyrochlore series minerals where Ca≥Na.

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Single crystals of K-priderites (K_x(M,Ti)₈O₁₆, M=Al, Fe and Mg) were grown from melts. Despite of the wide range of the solid solution the composition of all the single crystals obtained was around x=1.5. The prismatic faces of K–Al– and K–Mg-priderite consisted mainly of planes {100} with small {110} and those of K-Fe-priderite consist mainly of {110} with small {100}. The terminal faces of the crystals were made up of vicinal faces with irregular interfacial angle. The cleavage of the crystals was parallel to {110} on each priderite. Pleochroism of K–Al-priderite: O-colorless, E-blue; K–Fe-priderite: O-dark brown, E-dark brown with blue; K–Mg-priderite: O-pale blue, E-dark blue. The optical properties of Al₂TiO₅ and MgTi₂O₅ crystals included in priderite single crystals were also described.

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