a dense volcanic rock formed by the cementation of ash, scoria, lapilli, and other éjecta from an erupting volcano. Tuffs consist of fragments of volcanic glass, pumice, and other substances; tuffs composed of whole crystals or crystal fragments are also encountered.
Tuffs are classified according to composition, nature, and fragment sizes. In terms of composition, we distinguish among rhyo-litic, dacitic, andesitic, basaltic, and other tuffs. The color of tuffs varies; Artik tuff is violet-pink, and Ani tuff is orange or yellow (both types are found in the Armenian SSR). Tuffs are formed either by direct deposition from the air during a volcanic eruption or as a result of the transport of tuffaceous material by water or wind.
Tuff is a valuable building material of excellent ornamental quality. It is used, for example, as a filler in light concrete or as a wall material. In the USSR the main tuff deposits are in Armenia. In other countries the most important deposits are near Rome and Naples in Italy and in Iceland.
V. P. PETROV