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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).
An extrusive igneous rock with a very high silica content. 1  Rhyolite: A pink specimen of rhyolite with numerous very tiny vugs with some evidence of flow structures. 2  Igneous rock composition chart: This chart shows that rhyolite is typically composed of orthoclase, quartz, plagioclase, micas, and amphiboles.