蛇紋岩裂か中のセピオライト生成例

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In the course of field survey in Shigiyama area near Yawatahama, Ehime Prefecture, it was found that a clayey material with leather-1ike appearance occurred as a filling of fissures developed in a serpentinite. The "leather" was about 1 cm thick and grayish green or colourless, and exhibited fibrous texture. X-ray, thermal (DTA, TG, DTG), infrared, and electron optical analyses of the bulk sample and <2 μm size fraction separated have shown that the "leather" consisted principally of well-crystallized sepiolite ("α-sepiolite") with some calcite as an impurity. Elemental analysis of the <2 μm size fraction indicated Si and Mg as principal cations, and this result together with X-ray and thermal data fitted the Brauner-Preisinger model rather than the Nagy-Bradley one, giving a structural formula : (Mg_<7.63> Mn<0.02> Fe<0.28> Al_<0.06>) Si_<11.99> O_<30> (OH)_4 (OH_2)_4・9.12H_2O Minerals of MgO-SiO_2-H_2O system such as well- and poorly-crystallized serpentine, hydrated talc and stevensite have been formed, along with aragonite, as hydrothermal products witin the serpentinite. Such mineral association and published data of hydrothermal phase transition for sepiolite suggested that the sepiolite has been crystallized from low-temperature Mg soultion at the latest stage of hydrothermal process, according to the sequence, serpentine (chrysotile) → poorly-crystallized serpentine + hydrated talc → hydrated talc → stevensite → sepiolite.
日本粘土学会の論文
1984-05-31

蛇紋岩裂か中のセピオライト生成例

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