tuff

thumb|Cliff face of welded tuff pockmarked with holes — some natural, some man-made — from Bandelier National Monument, [[New Mexico]] thumb|Etruscan architecture|Etruscan tuff blocks from a tomb at [[Banditaccia, Italy]] thumb|upright|A house constructed of tuff blocks in Rieden, Rhineland-Palatinate, in the [[Volcanic Eifel region, Germany]]

Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash lithifies into solid rock. Rock that contains greater than 75% ash is considered tuff, while rock containing 25% to 75% ash is described as tuffaceous (for example, tuffaceous sandstone). A pyroclastic rock containing 25–75% volcanic bombs or volcanic blocks is called tuff breccia. Tuff composed of sandy volcanic material can be referred to as volcanic sandstone.