NEUES JAHRBUCH FUR MINERALOGIE-ABHANDLUNGEN, vol.189, no.1, pp.21-34, 2012 (SCI-Expanded)
The Arikli Tuff in the Behram Volcanics, NW Anatolia, is characterized by its dominance of authigenic analcime. It was studied by optical microscopy, XRD, SEM/EDX, and ICP for a better understanding of the analcime formation, which occurs as coarse-grained euhedral to subhedral crystals in pores and pumice fragments as well as in clusters or fine-grained single crystals embedded in the matrix. Besides analcime, K-feldspar, dolomite, and smectite are found as further authigenic minerals. Based on the dominance of these authigenic minerals, the tuffs are petrographically separated into phyllosilicate-bearing vitric tuff, dolomite-rich vitric tuff, and K-feldspar-dominated vitric tuff. No precursor of zeolites other than analcime was detected. Petrographical and SEM investigations indicate that euhedral to subhedral analcime crystals found as a coarse-grained filling cement in voids and pumice fragments are precipitated from pore water, whereas fine-grained disseminated crystals are formed by the dissolution-precipitation of glassy material. Hydrolysis of glassy material that is similar in composition to analcime provides the additional Na, Al, Si, and K elements which arc necessary for the formation of analcime.