The Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists
Online ISSN : 1883-0765
Print ISSN : 0021-4825
ISSN-L : 0021-4825
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Volume 59, Issue 4
Displaying 1-4 of 4 articles from this issue
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  • Petrogenesis of banded pumices from some volcanoes in Hokkaido, Japan
    Masaki Iwanaga
    1968 Volume 59 Issue 4 Pages 125-142
    Published: April 05, 1968
    Released on J-STAGE: August 07, 2008
    DOIhttps://doi.org/10.2465/ganko1941.59.125
    JOURNAL FREE ACCESS
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    It is well-known fact that two different magmas are extruded at the same time in some volcanoes and their products are frequently found to occur as banded pumice, consisting of pumice and socria. In the present paper, some exmaples of banded pumice from Komagatake, Tarumai and Daisetsu, active volcanoes in Hokkaido are introduced.
    There is no marked difference in petrography between pumice and scoria of augite-hypersthene andesite except for occurrence of some hornblende phenocrysts in the pumice of Daisetsu. However, it can be said with no exception that pumice is rich in SiO2, Na2O, and K20 and poor in FeO, Fe2O3, CaO, MgO, Ti02 and MnO as compared with socria. In the proportion between them, scoria occupies less than 10% (by volume) and commonly 5% (by volume) of whole products. There is a tendency that pumice is commonly ejected in the earlier stage, against scoria in the later stage and banded pumice is ejected at a period of transition from pumice to scoria. These facts suggest that the acidic magma forming pumice occupied the upper position of the magmatic body in its reservoir.
    The mechanism of formation of banded structure may result from that two different magmas were mechanically stretched in the process of rising through the narrow volcanic pipe from the magma reservoir. On the basis of fractional crystallization, it is impossible to give an adequate explanation of derivation of two magmas, therefore, other causes (e.g. liquid immiscibility, mixing of two original magmas or remelted products of accessory rocks) are also discussed for dissolving this problem.
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  • New mineral Akaganeite, β-FeOOH, from Akagane Mine, Iwate Prefecture, Japan
    Matsuo Nambu
    1968 Volume 59 Issue 4 Pages 143-151
    Published: April 05, 1968
    Released on J-STAGE: August 07, 2008
    DOIhttps://doi.org/10.2465/ganko1941.59.143
    JOURNAL FREE ACCESS
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    The new mineral akaganeite is beta-ferric oxyhydroxide from the weathered outcrop of the Akagane pyrometasomatic copper-iron deposit in Carboniferous green rock, Iwate Prefecture, Japan. The mineral is the supergene oxidation product of massive pyrrhotite and intimately associated with goethite, melantilite and two kinds of ferric sulfates. The mineral occurs in powdery aggregates of very fine orange to brownish-yellow crystals, elongated [001] and flattened (100) up to 0.3×0.03μ in size under the electron microscope.
    Two chemical analyses carried out in 1956 and 1959, respectively: Fe2O3 78.23, 80.98; FeO 0.82, 0.23; SiO2 3.10, 3, 57; A12O3 1.21, 1.40; Na2O 0.62, 0.82; K2O 0.19, 0.29; H2O+ 10.20, 9.71; H2O- 4.96, 2.55, sum 99.33, 99.55%. These data correspond closely to FeOOH. Chlorine was detected qualitatively, but material was in sufficient for a quantitative analysis.
    X-ray powder data are indexed on a tetragonal cell with a=10.50, c=3.03A. The strongest lines are 7.45 (98) (110), 5.31 (48) (200), 3.71 (21) (220), 3.34 (100) (310), 2.361 (33) (400), 2.553 (95) (211), 2.340 (8) (420), 2.300 (43) (301), 2.103 (31) (321), 1.954 ((39) (411), 1.750 (42) (600), 1.720 (12) (501, 431), 1.646 (52) (521), 1.520 (21) (002), 1.456 (28) (640), 1.441 (30d) (1.438), 1.381 (40d) (730, 312). These data agree very closely with the data obtained by Macky (1960), who showed the synthetic β-FeOOH is tetragonal, 14/m, a=10.48, c=3.023A. A DTA curve showed a slight endothermal reaction at about 300°C and a marked exothermal peak at 375°C. The mineral loss 11% in weight to 350°C, nearly all between 250 and 350°C.
    The name is for the mine. The mineral and name were aproved before publication by the Commission on New Minerals and Mineral Names, IMA.
    Two short communications on akaganeite have been described in Japanese by the present author (1957, 1960).
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  • Some rock-forming minerals of the cortlandtites from the Abukuma plateau
    Hitoshi Onuki
    1968 Volume 59 Issue 4 Pages 152-156
    Published: April 05, 1968
    Released on J-STAGE: August 07, 2008
    DOIhttps://doi.org/10.2465/ganko1941.59.152
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    Three clinopyroxenes, an orthopyroxene and a hornblende from the cortlandtite and associated mela-gabbros in the Abukuma plateau are chemically analysed. Fe+2-Mg partition coefficient between co-existing pyroxenes of the cortlandtite may be supposed to indicate lower temperature range of igneous crystallization.
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  • [title in Japanese]
    1968 Volume 59 Issue 4 Pages 162-173
    Published: 1968
    Released on J-STAGE: July 13, 2012
    DOIhttps://doi.org/10.2465/ganko1941.59.162
    JOURNAL FREE ACCESS
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