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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]
Tuffite is a tuff containing both pyroclastic and detrital materials, but predominantly pyroclasts. According to the IUGS definition, tuffite contains 75% to 25% volcanic (epiclastic) material. [1] There are several classifications that define tuffite. The classification in the IUGS recommendation is based on the definition established by ...
USGS scientist examines pumice blocks at the edge of a pyroclastic flow from Mount St. Helens Rocks from the Bishop Tuff, uncompressed with pumice on left; compressed with fiamme on right. Flight through a μCT-image stack of a lapillus of the volcano Katla in Iceland. Find spot: Beach near Vik at the end of road 215. Acquisition done using "CT ...
In igneous petrology, eutaxitic texture describes the layered or banded texture in some extrusive rock bodies. It is often caused by the compaction and flattening of glass shards and pumice fragments around undeformed crystals.
Welded tuff textures are distinctive (termed eutaxitic), with flattened lapilli, fiamme, blocks and bombs forming oblate to discus-shaped forms within layers. These rocks are quite indurated and tough, as opposed to non-welded lapilli tuffs, which are unconsolidated and easily eroded .
The Lava Creek Tuff is a voluminous sheet of ash-flow tuff located in Wyoming, Montana and Idaho, United States. It was created during the Lava Creek eruption around 630,000 years ago, which led to the formation of the Yellowstone Caldera. This eruption is considered the climactic event of Yellowstone's third volcanic cycle.
Fiamme in the Resting Spring Tuff near Shoshone, California. Rocks from the Bishop tuff, uncompressed with pumice on left; compressed with fiamme on right.. Fiamme are lens-shapes, usually millimetres to centimetres in size, seen on surfaces of some volcaniclastic rocks.
Texture is an important criterion for the naming of volcanic rocks. The texture of volcanic rocks, including the size, shape, orientation, and distribution of mineral grains and the intergrain relationships, will determine whether the rock is termed a tuff, a pyroclastic lava or a simple lava.