The growth mechanism and the growth condition of single crystals of aluminum nitride (AlN) prepared by the sublimation method are studied in relation with their morphology. The whiskers of AlN, whose growth directions are perpendicular to the (10-10) plane (a-type whiskers), the (10-11) plane (b-type whiskers) and the (0001) plane (c-type whiskers) grow through the VLS mechanism, iron acting as liquid-forming agent in the mechanism. The growth directions of whiskers depend on the growth temperature; the c-type whiskers grow above 1550°C, the a-type above 1700°C and the b-type above 1850°C. Blade-shaped crystals with large (0001) faces (a-type crystals) grow from lateral surfaces of the a-type whiskers.
Prismatic crystals with large prismatic (10-10) faces (P-type crystals) and tabular crystals with large (0001) faces (T-type crystals) grow above 1900°C in the atmosphere free from iron. The P-type crystals grow in the circumstance of high purity. The T-type crystals grow in the atmosphere comprising carbon mono-oxide.
Growth spirals are observed on the (0001) face of the T-type crystals. The growth steps parallel to the c-axis and a-axis observed on the (10-10) face of the P-type crystals.

View full abstract

Sulfides and oxides in pelitic schists of the Sanbagawa metamorphic terrain in the Shiraga-yama area, central Shikoku, Japan, are pyrrhotite, pyrite, chalcopyrite, ilmenite, and rutile. The most abundant assemblage of opaque minerals is pyrrhotite+pyrite+chalcopyrite in the chlorite zone and a lower-grade part of the garnet zone, and pyrrhotite+chalcopyrite+ilmenite+rutile+ (pyrite) in a higher-grade part of the garnet zone and the biotite zone. In this area, in addition to monoclinic Fe₇S₈ pyrrhotite which is common, intermediate pyrrhotite with Fe₉S₁₀ does occur, and also Fe₉Sio+pyrite assemblage is observed. This fact suggests that the Sanbagawa schists were metamorphosed above 310°C and that, although the majority of hexagonal pyrrhotite reacted with pyrite as cooling of metamorphic rocks proceeded, some pyrrhotite persisted to keep high temperature chemistry. It was also revealed by this study that pyrrhotites in the samples collected at the surface exposures are more or less oxidized but those collected from the drill cores are little oxidized.

View full abstract

The crystal structure of rankinite has been determined by Patterson and direct methods and refined to R=11.6%, using a crystal from Fuka, Bitchu-cho, Japan: P2₁⁄a, a 10.60(2), b 8.92(2), c 7.89(2)Å, β 119.6(1)°, Z=4 Ca₃Si₂O₇. There are in the structure arrays of Si₂O₇ groups parallel to the c axis, and the groups are linked together by Ca’s each having seven near oxygen atoms: the Ca–O bond length in the structure is in the range from 2.25 to 2.90 Å. Si–O is from 1.52 to 1.65 Å. The structural relationships between rankinite (Ca₃Si₂O₇) and kilchoanite [Ca₆(SiO₄)(Si₃O₁₀)] are described briefly.

View full abstract

The three-pyroxene assemblage, augite+orthopyroxene+pigeonite, has been observed in two different Japanese lavas of known crystallization temperatures. Based on the compositions of pyroxenes in these lavas and experimental data on the iron-rich inverted pigeonite, temperature of the lower stability limit of pigeonite (or “pigeonite eutectoid reaction line”) near 1 atm has been estimated; i. e., 1125°C, 1090°C and 1000°C for Fe/(Mg+Fe) ratios 0.300, 0.370 and 0.560, respectively. These temperature-composition relations are approximated by a line T=1270−480X_Fe (T is temperature in °C and X_Fe is atomic ratio Fe/(Mg+Fe)) and can be used as a geothermometer.

View full abstract

Manganobarian phlogopite and kinoshitalite, a barium brittle mica, from the Noda-Tamagawa mine, Northeast Japan, have an apparent solid solution series with a wide range of Ba content. The Ba content varies from 5.3 atomic percent to 55.6 atomic percent in the Na–K–Ca–Ba system.
Physical and optical properties change with the increase of Ba content in the manganoan phlogopite-kinoshitalite series : Specific gravity increases linearly. Birefringence decreases rapidly between 20.7 percent and 34.2 percent Ba, as the result of the increase of α.
Specimens containing as much as 34.2 percent Ba are brittle with smoother cleavage flakes and have lower birefringence (0.020) than manganoan phlogopite. Therefore manganoan phlogopite is thought to change into kinoshitalite at a composition near Ba:K=1:2.

View full abstract