The most common and well known member of the Rhyolite family is Obsidian. The most common and well known member of the Rhyolite family is Obsidian. Rhyolite is a comparatively common volcanic rock. It is the chemical equal of granite. Although the 2 rock types have the same chemistry, rhyolite is extrusive and granite is intrusive. While granite has crystals which can be generally obvious to see, in rhyolite the crystals are usually too small to see.