What is a tuff in geology ?

Tuff : definition

This term is used to designate two types of rocks of very different origins.

Volcanic tuff is a rock formed by the accumulation of volcanic fragments of a few millimeters, belonging to the family of pyroclastic rocks. The tuffs may contain larger fragments, even blocks, and have been consolidated under the action of water. Welded tuffs designate accumulations of hot welded incandescent lava debris.

Tuff is also used as a synonym for travertine (limestone tuff), to refer to the bedded hydrothermal limestones that are deposited at the emergences of hot springs.