Flattened, elongate, pumice clasts that are found in many welded ignimbrites. The pumice clasts, which are in a hot, plastic state when deposited from the pyroclastic flow, are compressed and flattened by the weight of the overlying ignimbrite body, producing elongated glassy clasts with ragged, flame-like ends (fiamme is the Italian word for ‘flame’). Many fiamme clasts continue to vesiculate after formation, leading to the development of spherical vesicles within them.