Existing comment:
Rhyolite:
Volcanic rocks which are chemically similar to granite are called rhyolites. Unlike obsidian or pumice, "stony" appearing rhyolites have cooled slowly enough to contain very small quartz and feldspar crystals, and few if any gas bubbles. They are generally light colored rocks often white, light pink, or red and are banded, showing the effects of movement as they cooled. Rhyolites with this "stony" appearance can be found in the Mono Craters. |