Linear patterns in a thunderegg agate from Oregon. Thundereggs are nodule-like rocks and are found in layers of rhyolitic lava flows. Image #3701
Macro photograph of linear patterns in a Whitcomb Creek geode from Oregon; a geode is a stone nodule with an inner cavity filled with crystals or mineral matter Image #3286
Macro photograph of the detail in a piece of Birds Eye rhyolite; a rock of volcanic origin; #2369
