Tuff
Introduction
The volcanic tuff, volcanic tuff or quarry (in Mexico) is a type of volcanic igneous rock, light, porous in consistency, formed by the accumulation of ash or other very small volcanic elements expelled from vents during a volcanic eruption.
It is formed mainly by the deposition of ash and lapilli during pyroclastic eruptions. Its cooling rate is faster than in the case of intrusive rocks such as granite and with a lower concentration of crystals. It should not be confused with calcareous tuff nor with pumice.
Constructive use
Tosca from the Canary Islands
Certain tuffs are known in the Canary Islands (Spain) under the name “toscas”. Its consistency is medium, which makes it ideal for stonework and, within it, for building troglodyte homes (such as the nucleus of Guayadeque in Gran Canaria). Its color ranges from red to white/yellow, the latter are those that come from "burning cloud" type eruptions and are called "white toscas", they are typical of the southeast of Tenerife.
Arequipa ashlar
In the south of Peru there are a large number of pyroclastic flow deposits that cover large extensions of the western Andean flank.[1] Some of these flows, under the name sillar or sillar stone, which is an exclusively local name for ignimbrite,[2] have been used extensively as construction material in the city of Arequipa and its surroundings in a construction tradition that dates back to the beginning of the Spanish colony. Due to the effect of pressure and temperature, the pyroclastic flows are devitrified and welded,[2] thus becoming ashlar, a pyroclastic rock of predominantly white to grayish color with homogeneous granularity.[1] This tone gives the main buildings in the historic center of the city of Arequipa a characteristic aesthetic and color, which is why the city is known by the popular nickname of City. Blanca.[3] The main outcrop and quarry of ashlar stone is located in the Añashuayco ravine,[1] at the foot of the Chachani volcano.