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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]
The La Cueva Member is an unwelded to poorly welded tuff with phenocrysts of quartz and sanidine and traces of pyroxene and magnetite. It has been divided into two units; [ 11 ] the upper unit is nonwelded to slightly welded and contains large pumice clasts, while the lower unit is nonwelded and includes abundant lithic fragments.
Phaneritic (phaner = visible) textures are typical of intrusive igneous rocks, these rocks crystallized slowly below Earth's surface. As magma cools slowly the minerals have time to grow and form large crystals. The minerals in a phaneritic igneous rock are sufficiently large to see each individual crystal with the naked eye.
Rhyolite is an extrusive igneous rock, formed from magma rich in silica that is extruded from a volcanic vent to cool quickly on the surface rather than slowly in the subsurface. It is generally light in color due to its low content of mafic minerals, and it is typically very fine-grained ( aphanitic ) or glassy .
Rocks from the Bishop tuff from California, United States, uncompressed with pumice on left; compressed with fiamme on right The caprock in this photo is the ignimbrite layer of the Rattlesnake Formation in Oregon. Ignimbrite is a type of volcanic rock, consisting of hardened tuff. [1]
The rhyolite tuff member is the lowest stratigraphic exposure of the Newbury Volcanic Complex. This member is made up of glassy fragments of rhyolitic tuff that is heavily sheared and is crudely held together and is about 6 m in thickness and yellowish-brown to brownish-gray in color. It is inferred that this member was deposited by an ash flow ...
Outcrops of Wall Mountain Tuff, one of the most widespread extrusive units of the CCVF, may be found near the town of Castle Rock, more than 90 miles (140 km) from the presumed eruptive source of the tuff. [3] Locally known as Castle Rock Rhyolite, the stone was quarried for dimension stone and construction aggregate beginning in 1872 and used ...
The Bishop Tuff is a welded tuff which formed 764,800 ± 600 years ago as a rhyolitic pyroclastic flow during the approximately six-day eruption that formed the Long Valley Caldera. [1] [2] [3] Large outcrops of the tuff are located in Inyo and Mono Counties, California, United States. Approximately 200 cubic kilometers of ash and tuff erupted ...