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RHYODACITE WELDED TUFF, IG-140N. Nevada. 35% of rock composed of fragmented crystals of quartz, sanidine and plagioclase with a few 1-5 mm black glass shards in compacted reddish brown glass. Near Currant, Nye County, Nevada. Check. RHYODACITE WELDED TUFF, IG-140O. Nevada. Large, light yellowish mottled areas in dark glass matrix. Thin section shows typical welding evidence and phenocrysts of plagioclase, quartz and mica with other minor minerals. Check. ALTERED RHYOLITE WELDED TUFF, IG-140P. Nevada. Megascopically prominent embayed quartz fragments and sanidine crystals, both around 3 mm, in very light brownish devitrified glass. Thin section shows welding deformation and altering of selected minerals together with fresh units to suggest sources differing in age. Check. DACITE WELDED TUFF, IG-140Q. Up to 3 mm labradorite, up to 2 mm biotite, up to 4 mm quartz, up to 1.5 mm sanidine megascopically visible in welded glass shard matrix with other less prominent minerals in thin section. Check. RHYOLITE WELDED TUFF, IG-140R. Megascopically the rock shows biotite and white feldspar in a light brown glassy matrix. Check. |