Zeolitized Tuffs and Occurrence of Ferrierite in Tadami-machi, Fukushima Prefecture

概要

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The Miocene formations in the Tadami area are chiefly composed of pyroclastic and volcanic rocks. Among them rhyolitic vitric tuffs of the Fuzawa formation are extensively altered to zeolite rocks with white colour. Volcanic glass in these tuffs is largely altered to zeolites, associated with opal, montmorillonite and secondary quartz, though the crystal fragments of feldspar and biotite are unaltered. Clinoptilolite and mordenite are the principal zeolites in the altered tuffs. Ferrierite also occurs as an alteration product of the volcanic glass. Glass shards are replaced by microcrystalline ferrierite and the vitroclastic texture is still preserved. The X-ray powder diffraction data of this ferrierite agrees well with that of ferrierite from Kamloops Lake, British Columbia.<BR>Ferrieritized tuffs are rarely intercalated as irregular thin bands or lenses in mordenitized tuffs of the lower part of the Fuzawa formation. Macroscopic and microscopic features of ferrieritized tuffs are similar that of mordenitized and clinoptilolitized tuffs.<BR>Ferrierite is a rare zeolite, which has been found so far only in cavity fillings in basaltic and andesitic rocks. Ferrierite from this area suggests its new mode of occurrence as a diagenetic alteration product of vitric tuff.
資源地質学会の論文