Mineralogical Journal
Online ISSN : 1881-4174
Print ISSN : 0544-2540
ISSN-L : 0544-2540
Volume 16, Issue 4
Displaying 1-3 of 3 articles from this issue
 
  • Sachinath MITRA, Tapan PAL, Prabal Kumar MAITY, Hi-Soo MOON
    1992 Volume 16 Issue 4 Pages 173-186
    Published: 1992
    Released on J-STAGE: March 31, 2007
    JOURNAL FREE ACCESS
    The compositions of the highly reflective zones (e.g., rim, patches, fractures, etc.) in chromites from two Indian chromite deposits (Sukinda and Nuggihalli schist belt) put them in the class of ‘ferritchromit’ and its ilk. EPMA study shows depletion of Mg, Al and enrichment of Cr, Fe from the host chromites to ferritchromit. The weakly anisotropic ‘ferritchromit’, however, hardly show any exsolution relationship with its host. High Fe3+/Fe2+ ratios in ‘ferritchromit’ determined from EPMA study are also found to have positive correlation with high Fe3+/Fe2+ values, as obtained from 57Fe Mössbauer spectroscopic study, of the bulk samples; all are suggestive of oxidation as the process causing ferritchromitization at any stage after the crystallization of chromites. The process of chemical transformation essentially involves the expulsion of Al, Mg and enrichment of Cr, Fe in these zones. The causative force arises out primarily from release of electron during oxidation and relaxation of the inbuilt lattice strain and transition from a perfectly cubic to a lower symmetry. The progress of work on this problem of ferritchromitization has been reassessed in the light of the present observations on samples from widely separated tectono-stratigraphic horizons of India.
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  • Tsutomu KAWAMURA
    1992 Volume 16 Issue 4 Pages 187-200
    Published: 1992
    Released on J-STAGE: March 31, 2007
    JOURNAL FREE ACCESS
    This paper gives a method of the specimen preparation for the in situ observation at high temperatures by X-ray diffraction. This method is very simple and needs not the special instrument. This method is, however, much effective to the semiconductor wafers, particularly to the III–V compound semiconductor wafers, which have high vapor pressures near at the melting points, such as InP, GaAs and GaP. The melting points of the wafers are reported as 1060, 1240 and 1465°C, respectively. This method can be applied to these wafers without destructing these specimens, even at such high temperatures near the melting point.
    A few experimental results using this newly devised method are presented.
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  • Koichi WATANABE, Masao KITAMURA
    1992 Volume 16 Issue 4 Pages 201-214
    Published: 1992
    Released on J-STAGE: March 31, 2007
    JOURNAL FREE ACCESS
    Growth mechanism of plagioclase crystals from a basaltic melt of tholeiite type prepared by chemical reagents was studied by using the isothermal-dropping technique with iron and platinum capsules. Produced phases are plagioclase, olivine, pigeonite and augite. Crystal morphology of plagioclase varies from prismatic to spherulitic with increasing degree of undercooling, ΔT.
    Crystal length along the elongated direction of plagioclase increases with the square root of time, and the normal growth rates are in the range of about 0.2−13.0×10−3 (mm/min) at ΔT of 9–95°C. At ΔT less than 30°C, the spiral or two dimensional nucleation mechanism is dominant. At ΔT between 30 and 70°C, two-dimensional nucleation, and at ΔT more than 70°C, diffusion controlled continuous or non-faceted growth mechanisms are dominant.
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