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lithic fragment The dense or crystalline components of a pyroclastic deposit. Three types are recognized. Cognate lithics are fragments of non-vesiculated, juvenile, magmatic material, e.g. dense, angular, glass fragments. Accessory lithics are fragments of country rocks ejected explosively during eruption. Accidental lithics are clasts picked up locally by pyroclastic flows and surges. Lithics range from blocks to ash-size fragments and are usually angular, but may be rounded by in-vent abrasion during eruption.