1. Education

Thunderegg

Official State Rocks and State Stones of the United States

By

The thunderegg is the state rock of Oregon. The agate lumps form by deposition of silica in openings in thick beds of rhyolite lava, in Oregon and other states.
OR
Photo (c) 2007 Andrew Alden, licensed to About.com (fair use policy)
Top Related Searches

©2014 About.com. All rights reserved.