pyroclastic

adjective

composed chiefly of rock fragments or particles of volcanic origin, such as pumice, obsidian, or volcanic ash

Etymology: From pyro- + clastic, from Ancient Greek πῦρ (pûr, “fire”), and κλαστός (klastós, “broken”).

Mostly composed of rock fragments of volcanic origin or comminuted during an eruption.
“The word "ash" is not a very good one to include all the mechanical accompaniments of a subaerial or subaqueous eruption, since ash seems to be restricted to a fine powder, the residuum of combustion. A word is wanting to express all such accompaniments, no matter what their size or condition may be, when they are accumulated in such mass as to form beds of "rock." We might call them perhaps "pyroclastic materials," ...”
“Within sixty seconds, the entire area was razed by pyroclastic material with a temperature of nearly two thousand degrees Fahrenheit.”

Etymology: From pyro- + clastic, from Ancient Greek πῦρ (pûr, “fire”), and κλαστός (klastós, “broken”).

A rock mostly composed of rock fragments of volcanic origin.
“The basic volcanics are altered andesites, porphyritic diabases and andesites, and various pyroclastics.”