Pumice Stone au natural

Mono Lake May 26, 2013 Pumice stone found at the Mono Lake Visitor's Center Inscription states: "Pumice is the name given to highly porous obsidian. It forms when a rhyolitic lava containing dissolved gases erupts on the surface. During eruptions, bubbles form in much the same way they do when a soda bottle is opened. Rapid cooling of the lava traps the bubbles before they can escape. Pumice can be found in the Mono Craters and on the ground over much of the Scenic Area. It has commercial value and is mined from the Mono Craters."