Rhyolitic Breccia, West Yellowstone, Montana, U.S.A.
Building Image
 
      Any American tourist attraction has to have a T-shirt shop, and so Yellowstone National Park has this one in West Yellowstone, Montana. It's built of a rhyolitic breccia, a volcanic rock in which chunks of pre-exisiting volcanic rock (the dark spots) were incorporated (see below). Much of the Yellowstone country consists of volcanic rock, mostly rhyolite, and this particular variety tells an interesting story of an eruption that swept up earlier volcanic fragments and made them part of this entire rock.

 
Stone Image

 


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