"Wonder Stone" A type of Rhyolite:
Rhyolite is a light-colored rock with silica (SiO2) content greater than about 68%. Sodium and potassium oxides both can reach about 5%. 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.
The word rhyolite comes from the Greek word for stream (rhyax) + the suffix lite. Rhyolite was named streaming rock because of its beautiful flow bands, which are made of bubble and crystal rich layers that form as the lava flows onto the surface and advances.
Rhyolite can look very different, depending on how it erupts. Explosive eruptions of rhyolite create pumice, which is white and full of bubbles. Effusive eruptions of rhyolite often produce obsidian, which is bubble-free and black.
The colour of rhyolite ranges widely, but generally is white or light yellow, brown, or red. Most rhyolites are flow banded; that is, they show streaky irregular layers that are formed by the flowing of the sticky, almost congealed magma.
Wonder Stone or Wonder Rock is a common name for a tight graned type of Rhyolite, that is suitable for gemstone use. This rhyolite is banded and has very pleasing colors of plumb, yellow and tans.Wonder rock is found in many locations thorough the west. (for example, Yellowstone in Wyoming, Long Valley in California, Alder, Montana and Valles in New Mexico)
The better veriies of Wonder Rock come from the Montana and Wyoming sites. Alder Montana is located in Madison County 9 miles W of Virginia City along Highway 287 near Beaverhead National Forest and Ruby River Reservoir.