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Rhyolite caldera complexes are the most explosive of Earth's volcanoes but often don't even look like volcanoes. They are usually so explosive when they erupt that they end up collapsing in on themselves rather than building any tall structure (George Walker has termed such structures inverse volcanoes).
The glassy rhyolites include obsidian, pitchstone, perlite, and pumice. The chemical composition of rhyolite is very like that of granite. The phenocrysts of rhyolite may include quartz, potassium feldspar, plagioclase feldspar, biotite, amphibole, or pyroxene.ertain differences between rhyolite and granite are noteworthy. Muscovite, a common mineral in granite, occurs very rarely and only as an alteration product in rhyolite. In most granites the potassium feldspar is microcline or microcline-perthite; in most rhyolites, however, it is sanidine.