Strongly Welded Rhyolite Tuff
Each of Yellowstone's three major eruptions produced huge flows of hot debris that formed thick hot deposits. The deposit interiors were hot enough to compress, squeezing once-rounded pumices into flattened disks, such as in this strongly welded tuff.
Time Period: Erupted 2.1 million years ago
Loaned by Yellowstone National Park
Locality: Yellowstone National Park