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Tuff

Aslo called welded tuff. A cemented mass of tephra with up to 50 percent sediments mixed. Tuff is a pyroclastic rock composed mostly of angular fragments of volcanic material deposited from the air. If deposited on land while hot, the particles weld together as a welded tuff; otherwise, normal lithification occurs.

Tuff (from the Italian "tufo") is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. (Note that tuff is a type of rock entirely different from tufa.)

Welded tuff is basically a product of pyroclastic flows hot enough to fuse or "weld" still-hot ash into a single uniform layer called a cooling unit. Ignimbrite is another term commonly used for this type of tuff. The glass fragments that make up much of the erupted ash flow and deform readily, and their curving shapes are flattened and deformed during the welding process (see image and contrast with the ash shapes in unwelded tuff).

Welded tuff deposits can be highly voluminous, such as the Lava Creek Tuff erupted from Yellowstone Caldera in Wyoming 640,000 years ago. Lava Creek Tuff is known to be at least 1000 times as large as the deposits of Mount St. Helens's May 18, 1980 eruption, and it had a Volcanic Explosivity Index (VEI) of 8 -- greater than any eruption known in the last 10,000 years. Such deposits may be represented by welded tuff near the eruption source, tuff at greater distances, and unconsolidated ash yet further away. Welded tuff is commonly rhyolitic in composition.

Material Notes:
Kao-Tuff C is an abrasion resistance castables, installed by using standard vibratory casting techniques. The high strength consistently produce abrasion losses in range of 8-15 cc’s.

Tuff is a volcanic rock, deriving from magma. The loose fragments, if less than 2 mm in diameter, are called ash. When the ash is consolidated and cemented into rock it is called tuff. The Egyptian word bxn may include this stone: see also siltstone.

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