Welded tuff (western USA), (public display, Geology Departm…

(public display, Geology Department, Wittenberg University, Springfield, Ohio, USA) ----------------------------------- Igneous rocks form by the cooling & crystallization of hot, molten rock (magma & lava). If this happens at or near the land surface, or on the seafloor, they are extrusive igneous rocks. If this happens deep underground, they are intrusive igneous rocks. Most igneous rocks have a crystalline texture, but some are clastic, vesicular, frothy, or glassy. Volcanic tuffs are solidified ash deposits - they form by explosive volcanic eruptions, as do volcanic breccias. Volcanic tuffs lack the abundance of large, angular grains present in volcanic breccias (although I

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