Home – Home – Jornals – Russian Geology and Geophysics 2018 number Неопубликованное

The morphology, species, and chemical composition of zeolites in agates from the Tevinskoye and Kinkilskoye deposits (Western Kamchatka, Russia) were studied in detail for the first time. Optical and scanning electron microscopy, EPMA, X-ray diffraction analysis, Raman spectroscopy, and X-ray computed microtomography were used. High-silica zeolites have been identified: clinoptilolite-Ca, clinoptilolite-Na, heulandite-Na, heulandite-K and mordenite. Agates from the Tevinskoye deposit were identified as intergrowths of orange and colorless prismatic clinoptilolite-Na crystals, forming a continuous rhythm up to 0.5 mm thick at the contact zone between the agate and the host rock. Numerous mordenite spherulites formed by radially radiating fine-acicular crystals approximately 1 mm long and rare intergrowths of prismatic clinoptilolite-Ca, clinoptilolite-Na, heulandite-Na, heulandite-K crystals were also diagnosed at the boundary between the agate and the host rock from the Kinkilskoye deposit. A typomorphic feature of clinoptilolite and heulandite in agates from both deposits is the admixture of BaO (0.22 to 0.73 wt.%). Silica minerals in the agates are represented by low-temperature cristobalite, chalcedony, quartzine, moganite, microgranular and coarse-crystalline quartz, including amethyst. The presence of "immature" forms of silica — moganite and low-temperature cristobalite — in the studied agates is associated with the young (Eocene) geological age of the volcanic formations. The formation of zeolites in the Tevinsky and Kinkilsky agates could have occurred with the participation of thermal neutral or alkaline. Crystallization of zeolites on the walls of gas cavities apparently occurred from supersaturated (Al, Na, K, Ca, Ba) aqueous solutions and preceded the precipitation of silica.