Vesicular Rhyolite

Mohs hardness of 6-7, typically light-colored (tan, pink, or gray due to high silica), earthy to vitreous luster, fine-grained groundmass with visible gas bubbles (vesicles), specific gravity of 2.4-2.6.

Formed from the rapid cooling of high-viscosity, silica-rich lava at or near the Earth's surface. The pits or holes (vesicles) are created by trapped gas bubbles that escape as the lava solidifies. It can range in age from very recent to hundreds of millions of years.

Used as decorative stone in landscaping, as an abrasive in industrial settings, and as an aggregate in lightweight concrete construction.

Rhyolite is the volcanic equivalent of granite. It is so thick and sticky when it flows that it often traps gases, leading to the highly textured, bubbly surface seen in specimens like this.

Identify in the field by its light weight (due to vesicles), light color, and the presence of small holes. Commonly found in volcanic regions such as the American West, Iceland, and New Zealand.