Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock.[1][2] 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).[3]

Welded tuff from Bandelier National Monument, New Mexico
Etruscan tuff blocks from a tomb at Banditaccia
A tuff house in Germany

Tuff is a relatively soft rock, so it has been used for construction since ancient times.[4] Because it is common in Italy, the Romans used it often for construction.[5] The Rapa Nui people used it to make most of the moai statues on Easter Island.[6]

Tuff can be classified as either igneous or sedimentary rock. It is usually studied in the context of igneous petrology, although it is sometimes described using sedimentological terms.

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