Journal of Mineralogical and Petrological Sciences
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Volume 112 , Issue 3
June
Showing 1-4 articles out of 4 articles from the selected issue
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ORIGINAL ARTICLES
  • Satomi ENJU, Seiichiro UEHARA
    Volume 112 (2017) Issue 3 Pages 109-115
    Released: July 01, 2017
    JOURNALS FREE ACCESS

    Abuite was found in hydrothermally altered rocks in the Hinomaru–Nago mine, Kiyo area, Abu, Abu County, Yamaguchi Prefecture, Japan (34°53′N 131°52′E). Abuite is often included in aluminum phosphate rich samples, embedded with quartz and augelite and/or trolleite, and is often accompanied by other phosphates especially apatite and crandallite. Abuite is transparent and colorless with white streak and vitreous luster. It is very difficult to find them in bare eyes, since the dominant phases in aluminum phosphate rich samples, augelite, trolleite, and quartz, are all also transparent and colorless. The empirical formula of abuite (based on 10 anions pfu, O = 8, F + OH = 2) is (Ca0.99Sr0.01)1.00Al1.96P2.03O8(F1.89OH0.11). H2O was calculated by stoichiometry. The simplified formula is CaAl2(PO4)2F2. Abuite is the calcium analogue of SrAl2(PO4)2F2, which was synthesized by hydrothermal methods (Le Meins and Courbion, 1998). The crystal structure is orthorhombic, with space group P212121. Unit cell parameters refined from the obtained X–ray diffraction pattern are a = 11.818(2), b = 11.993(3), c = 4.6872(8) Å and V = 664.3(2) Å3, with Z = 4.

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  • Terumi EJIMA, Mari YONEDA, Masahide AKASAKA, Hiroaki OHFUJI, Yoshiaki ...
    Volume 112 (2017) Issue 3 Pages 116-126
    Released: July 01, 2017
    JOURNALS FREE ACCESS

    Mineral precipitates within olivine grains are a sensitive recorder of the oxidation conditions of scoria. The crystallization process of precipitates within olivine phenocrysts in andesitic scoria from Kasayama volcano, Hagi, Yamaguchi Prefecture, Japan was investigated. Electron microprobe analysis and Raman spectroscopy were used for mineral identification and electron back–scattered diffraction to determine the crystallographic orientation of the precipitate minerals and host olivine phenocrysts. The scoria in the interior of the Kasayama scoria cone is red–brown, and the outer surface of the cone is black or black with red–brown tint. The olivine phenocrysts (Fo79–81) within the black scoria lack precipitate minerals, but those in the black scoria with red–brown tint (Fo82–85) contain small amounts of precipitates at their rims, and those in the red–brown scoria (Fo99) contain abundant cryptocrystalline precipitates, including hematite and enstatite. Vermicular rods of hematite and enstatite form symplectite zones on the rims, and symplectite domains in the cores of the phenocrysts. The host olivine and the hematite precipitates have a crystallographic relationship of [100]Ol//[0001]Hem, [010]Ol//[1010]Hem, and [001]Ol//[2130]Hem, which is characteristic of olivine and precipitate minerals generated by high–temperature oxidation. The maximum oxidation temperature is estimated to be >800 °C. High temperature oxidizing conditions may have been maintained in the inner wall of the scoria cone because the scoria that erupted early in the sequence was deposited in the presence of air and was subsequently covered by black scoria making up the outer wall of the cone.

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LETTERS
  • Yumiko TSUBOKAWA, Masahiro ISHIKAWA
    Volume 112 (2017) Issue 3 Pages 127-131
    Released: July 01, 2017
    JOURNALS FREE ACCESS

    The sintering behavior of diopside nano–sized powder was studied. We successfully fabricated diopside nano–sized powders from naturally occurring diopside single crystal (Ca0.92Na0.07Mn0.01Mg0.93Fe0.01Al0.06Si2O6). Diopside polycrystalline is sintered from powders with an average particle size of <100 nm under argon flow at temperatures ranging from 1130–1280 °C for 0.5–20 h. The average grain size increased with increasing sintering time and sintering temperature while porosity remained nearly constant value of 3–4 vol%. The experimental data of grain growth at 1180 °C can be fit for the following equation G3G03 = kt, where G is the grain size after time t, G0 is the grain size at t = 0, and k is a rate constant.

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  • Kazuki TAKAHASHI, Toshiaki TSUNOGAE
    Volume 112 (2017) Issue 3 Pages 132-137
    Released: July 01, 2017
    JOURNALS FREE ACCESS

    A garnet–pyroxene granulite from Austhovde in the Lützow–Holm Complex, East Antarctica, contains two types of fluid inclusions: a small number of primary inclusions in garnet and quartz, and dominant secondary inclusions in garnet and plagioclase. The melting temperatures of the trapped fluids lie in a range of −57.2 to −56.4 °C, which are close to the triple–point temperature of pure CO2. The primary inclusions are homogenized at +1.8 to +12.6 °C, which correspond to densities of 0.842–0.917 g/cm3. However, the estimated pressure conditions (3–5 kbar at 850 °C) from the fluid densities of the primary inclusions are not consistent with the peak P–T conditions recorded in the rock (840–860 °C and 8.3–8.7 kbar). Homogenization of the secondary inclusions into the liquid phase occurs within a range of +11.5 to +25.2 °C, which correspond to low CO2 densities of 0.708 to 0.851 g/cm3. The results imply that fluid density decreased by partial leakage of the trapped fluid in the primary inclusions during post–peak exhumation stage, and the process is consistent with the occurrence of orthopyroxene + hornblende + plagioclase symplectite around garnet, suggesting post–peak rapid decompression.

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