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Volume 68, Issue 11
Displaying 1-4 of 4 articles from this issue
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Hajime Takamura1973 Volume 68 Issue 11 Pages 329-340
Published: November 05, 1973
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSMany andesitic lava flows of the calc-alkaline rock series erupted during the middle to late Miocene time are distributed in the western part of the Setouchi Inland Sea volcanic province. They cna be divided into the following three stages: 1) glassy andesitic and biotite dacitic, dykes 2) hornblende bearing andesitic laves and their pyroclastics, and 3) andesites forming domes or lavas and their pyroclastics.
Porphyritic andesites are characterized by high MgO content, though calculated groundmass compositions as well as aphyric andesites reveal the nature of the common Japanese calc-alkaine series.
MgO-FeO+Fe2O3-Na2O+K2O diagram shows that these andesitic rocks are chemically divided into MgO-poor and MgO-poor and MgO-rich groups. The former group carries granitic xenolith, indicating the effect of contamination.View full abstractDownload PDF (588K) -
RYOHEI OTSUKA, SADAO TSUTSUMI, TAKABUMI SAKAMOTO, KUMIKO KANDA1973 Volume 68 Issue 11 Pages 341-345
Published: November 05, 1973
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESS -
Kazuo Yamaoka, Hiroshi Utsugi1973 Volume 68 Issue 11 Pages 346-352
Published: November 05, 1973
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThe amorphous silica deposit formed as masses near the surface at the southern foot of Mt. Arawo-dake occurs in the mudstone of Uppermost Miocene-Pliocene age. Various minerals such as kaolinite, opal, and alunite which are characterized by acid alteration occur around and within the silica deposit. A small amount of sulphur is sublimated in the fissures and cracks in the silica ores. The silica ores contain 80 to 96 percent of SiO2 (in dry matter), and are almost soluble by two normal NaOH solution at 100°C.
This deposit is considered to have been formed by the action of strong acid fluid containing a large amount of sulphuric acid and to be related with recent volcanism.
The characteristic features of the amorphous silica ore from Oni-kobe are discussed, and it is concluded that amorphous silics is composed essentially of “xerogel”.View full abstractDownload PDF (1118K) -
JUJIN SUZUKI, MASAHIRO ITO1973 Volume 68 Issue 11 Pages 353-361
Published: November 05, 1973
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSAn unusual magnesium carbonate hydrate mineral, Mg5 (CO3)4 (OH)2•8H2O, was found as encrustments of snow-white oolitic, botryoidal and reniform aggregates on the weathered surface of the brucite-bearing serpentinites from Yoshikawa, Aichi Prefecture, Japan. The empirical formula is similar to that of hydromagnesite except its having more H2O contents. Individual grains of the mineral are flaky and slightly soluble in distilled water.
This mineral has a long spacing of 33.2Å, which decreases gradually with rising temperature and completely disappears on heating up to 150°C. The long spacing does not expand with ethylene glycol. X-ray diffraction and infrared spectrum patterns for the 150°C-heated sample are similar to those for hydromagnesite.
DTA curve for this mineral shows five endothermic reactions with maxima at 40, 114, 270, 410, and 515°C, and an exothermic reaction at 496°C. The first two endotherms are considered to be caused by removal of interlayer water yielding the superlattice structure.
The optical properties are as follows: α=1.515, β=1.521, γ=1.522, and 2V (-)=44.5° (calculated).View full abstractDownload PDF (2255K)
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