NEW OCCURRENCE AND MINERALOGICAL PROPERTIES OF IRON-SEPIOLITE

概要

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Iron-sepiolite occurs in a dolomite deposit of the Kasuga mine, Gifu Prefecture, Japan. This sepiolite shows a dark brown colour on newly exposed surfaces, which, however, easily turns to brown when exposed to the air. It is pleochroic with brown to yellowish brown, and the refractive indices α=1.508 and γ=1.525,which are higher than those of magnesium-sepiolite. The lattice parameters of iron-sepiolite are a_0=13.74Å, b_0=26.97Å and c_0=5.28Å. The X-ray powder pattern consists of well-defined peaks. The thermogravimetric curve of iron-sepiolite shows a continuous weight loss with the removal of zeolitic water and of hydroxyl groups leading to formation of a completely dehydrated phase. The peaks on the differential thermal analysis and the derivative thermogravimetric curves due to the removal of the bound water and dehydroxylation are extremely weak. The weight loss of iron-sepiolite resulted from the removal of both zeolitic water and bound water is close to that of magnesium-sepiolite, whereas the weight loss due to dehydroxylation is smaller in iron-sepiolite than magnesium-sepiolite. This is probably due to secondary oxidation of iron in the former. A reasonable structural formula of iron-sepiolite was obtained by converting all ferric iron to ferrous iron.
日本粘土学会の論文