Slightly Welded Rhyolite Tuff

In the last 2.1 million years, three enormous eruptions have occurred in and near Yellowstone National Park. Each produced huge flows of hot debris that came to rest to form hard volcanic rocks like this tuff.

Group: Igneous
Time Period: Erupted 0.6 million years ago
Loaned by Yellowstone National Park
Locality: Yellowstone National Park , Wyoming