Crystal size distribution (CSD) was measured for plagioclase and pyroxenes in an andesite lava (Togawa lava), 40-60 m in thickness, of the Aso volcano, Kumamoto, Japan. The CSD was shown to have near linear relationships between logarithmic population density and crystal size. Solidification time was estimated for the lava solving thermal diffusion equations considerable latent heat of fusion. Comparing the CSD data at various depths of the lava, crystal growth rate was estimated to be in the range of 2.1〜6.9×10
-10mm/s. Significance of distinction between phenocryst and groundmass is discussed, which was not considered in Marsh (1988) and Cashman and Marsh (1988).
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