Rhyolite has many resemblances to granite! Rhyolite has many different ways of forming from highly viscous lava or in volcanic plugs and dikes. If the lava cools too quicky to grow crystals they form a natural glass that is known about obsidian. Slower cooling forms small crystals in the lava that results in different structures in the Rhyolite.
Only three eruptions of rhyolite have been recorded since the start of the 20th century, the majority of rhyolite is much, much older.