The occurrence and its chemical composition changes in the Dobuyama montmorillonite deposit, Miyagi Prefecture

Joyo Ossaka, Jun-ichi Hirabayashi, Kiyoshi Okada, Masahiro Kato
1981 Journal of the Mineralogical Society of Japan  
Changes of chemical compositions and minerals in alteration process which seems to take place in slightly alkaline conditions under the earth surface and forms montmorillonite as an alteration product were examined. Specimens at various stages of alteration were collected from Dobuyama mine, Miyagi Prefecture considered to be formed by the hydrothermal alteration of rhyolitic pumice tuff. These specimens were investigated by the chemical analysis, X-ray diffraction, DTA, polarizing microscope,
more » ... EM and so on. It was found that primary minerals of quartz and feldspar almost disappeared and secondary minerals of montmorillonite and cristobalite crystallized by alteration. The chemical formula of this montmorillonite was determined to be ( Ca0.34 Na0.02 K0.01 Mg0.05) (Mg0.84 Fe3+0.16 Fe 2,0.09 A12.89) Si8.04 O20 (OH) 4 nH2O by chemical analysis. By alteration, SiO2, Na2O K2O and TiO2, were leached but A12O3 was a little leached. Fe203, and CaO were relatively concentrated and MgO was remarkably concentrated. This high concentration of MgO suggests the addition from solution. It was also found that montmorillonite in the upper zone of mine changed into kaolin-montmorillonite mixed layer minerals by weatherings under surface condition.
doi:10.2465/gkk1952.15.special_170 fatcat:q2xanufxvzb5thswicp6o5fi5q