A rock composed of pyroclastic materials that have been ejected from a volcano. In many instances these fragments are still hot when they land, producing a “welded” rock mass. Tuff is rock debris consisting of volcanic ashes and igneous rocks of fine- grained material. Consolidated volcanic ash, composed largely of fragments (less than 4 millimeters) produced directly by volcanic eruption; much of the fragmented material represents finely comminuted crystals and rocks.
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