(c) 2008 Andrew Alden, licensed to About.com (fair use policy)
Fiamme ("fi-YAHM-ay"), from the Italian word for flames, are a structure found in welded tuff. Welded tuff is a pile of volcanic material so hot that it fused together into rock after falling to the ground. Fiamme are small, dark lenses of glassy material thought to represent bits of pumice that were softened and compressed into the tuff during this welding episode. A tuff with fiamme is said to have flame structure. A single "flame" is a fiamma, and a fiamme-bearing tuff may be called a piperno ("pi-PAIR-no") if you feel like showing off.