Adjective

(-)

(vulcanology) Mostly composed of rock fragments of volcanic origin or comminuted during an eruption.

*{{quote-book

, year= 1862 , year_published= , author= , by= , title= The Student's Manual of Geology , url= http://books.google.com/books?id=3DUDAAAAQAAJ&pg=PA68 , original= , chapter= Igneous Rocks , isbn= , edition= 2 , publisher= Adam and Charles Black , location= Edinburgh , editor= , volume= , page= 68 , passage= 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," ... }}