Iron-sepiolite from the Seikan Tunnel, Japan.

概要

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A dark-brown scaly material was found in the pilot tunnel of the Seikan Tunnel. Our mineralogical work has clarified that this material consists largely of iron-sepiolite. The structural formula calculated on the basis of 32 oxygens in the half-unit cell of dehydrated sepiolite is as follows. (Si11.49Ti0.03Al0.38Fe3+0.10)12.00(Fe3+1.25Fe2+0.26Mn0.02Mg6.00)7.53O32•Ca0.03Na0.05K0.04 If the Fe ions are treated as being wholly Fe2+, the following formula will be obtained on the basis of O30(OH)4. (Si11.74Ti0.03Al0.23)12.00(Al0.16Fe2+1.65Mn0.02Mg6.13)7.95O30(OH)4•Ca0.03Na0.05K0.04 This modified formula coincides well with the theoretical one in respect to the numbers of octahedral and tetrahedral cations. Therefore it may be suggested that this sepiolite has been formed primarily as a ferrous-sepiolite and then oxidized in the air-exposed condition. In addition, mineralogical data such as X-ray diffraction, thermal analysis, etc., are presented.
日本鉱物科学会の論文