Rhyolite

Flow banding in rhyolite lava from Mono-Inyo Craters volcanic chain, California (black bands composed of obsidian)

Volcanic rock (or lava) that characteristically is light in color, contains 69 percent silica or more, and is rich in potassium and sodium.

Rhyolite is a light-colored rock with silica (SiO2) content greater than about 68 weight percent. Sodium and potassium oxides both can reach about 5 weight percent. Common mineral types include quartz, feldspar and biotite and are often found in a glassy matrix. Rhyolite is erupted at temperatures of 700 to 850 °C.