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What is tuff?

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Welcome to CoreFacts, where we're always short on time and big on science. I'm Brian Campbell. Today's question is …

What is tuff?

Tuff is a volcanic rock made up of a mixture of volcanic rock and mineral fragments in a volcanic ash matrix. Wherever there are explosive volcanic eruptions you can expect to find tuff. Tuff forms when some combination of ash, rock and mineral fragments (pyroclastics or tephra) are blasted into the air, then fall to the ground as a mixed deposit. Most of the rock fragments tend to be volcanic rocks that were once solidified parts of the volcano that erupted to produce the tuff, but sometimes other types of rock are blasted out and incorporated into the tuff as well.

And now you know.  Join us again every week for a new CoreFact.  For other CoreFacts, or for CoreCast, our in-depth science podcast, go to  If you’d like to have a question featured on our show, give us an e-mail at or a phone call at 703-648-5600.  Remember, long distance fees do apply.  CoreFacts is a product of the U.S. Geological Survey, Department of the Interior.

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Title: What is tuff?


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Date Recorded: 6/24/2009

Usage: This audio file is public domain/of free use unless otherwise stated. Please refer to the USGS Copyright section for how to credit this audio.

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