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Prol Ledesma, R. M.; Medina, F.; Choporov, D. Y.; Frikh K., D. I.; Muravitskaya, G. N.; Polak, B. G.; Stepanets, M. I. Preliminary Chemical and Petrographic Results of the March-April "El Chichon" Volcanics. Geofis Int 1982, 21, 1-10.