Rhyolite is a volcanic acid extrusive rock whose mass is greater than 66 silicaformed from the cooling of viscous lava. Because this lava flows slowly, it often blocks the crater, causing a build-up of gas pressurefinally ejecting from the crater with explosive force. Rhyolite is an acidic rock that often invades in the form of dikes. This kind of rock is only found in Huayu in Penghu. The active age of Huayu volcano may have been in the Cretaceous period of the late Mesozoicthe mid-Jurassic period,after the effect of hot water mass exchange, rhyolite has mottledrhyolite structures with a variety of colors, including gray-yellow, green, gray-purplegray-white. Its chemical composition is the same as that of granite. Part of it has vitreous lustercleavage due to its rapid cooling rate during formation, making the minerals too late to crystallize. The specimens collected by this center are from Huayu.