Caに富む25Å鉱物

概要

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Several samples of regularly interstratified Ca-rich 25A minerals of hydrothermal origin from two roseki deposits were examined by chemical analysis, X-ray diffraction and IR spectroscopy together with a few rectorites. These sampls are rich in SiO_2,Al_2O_3 and H_2O which are accompanied by considerable amounts of CaO, Na_2O and K_2O. Interlayer cations of mica-like layers are composed of a considerable amount of Ca. Ca populations are clearly greater than a half of all interlayer cations in mica-like layers and such a sample has not been reported so far. Al-for-Si substitution in the tetrahedral sheets of mica-like layers increases in proportion as Ca contents increase. The characteristic absorption bands of 950-900 cm^<-1> and 700-670 cm^<-1> are observed in IR spectra. The bands are due to Al-for-Si substitution in the tetrahedral sheets. Judging from the chemical analysis and IR spectra, the component of mica-like layer rich in Ca is not that of mica but mainly that of brittle mica (margarite). Expansion characteristics of the Ca-rich 25A mineral are similar to those of rectorite and expandable layer is close to beidellite. The mineral is somewhat less expandable that rectorite under the conditions of RH70-80% (Na-saturation) and EG treatment (K-saturation). The Ca-rich 25A mineral reported here is similar to rectorite in its expansion chractristics, but the component of mica-like layers of it is differnt from that of rectorite. Mica-like layer of the mineral must be mainly composed of margarite-1ike layer. The mineral is mainly composed of 1 : 1 regular interstratification of dioctahedral brittle mica (margatite) and smectite (beidellite). The mineral dose not strictly correspond to rectorite which is defined as 1 : 1 interstratified mineral of dioctahedral mica and smectite.
日本粘土学会の論文
1990-02-27

著者

松田敏彦
岡山大学理学部

Caに富む25Å鉱物

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