Rhyolite
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Rhyolite is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained in texture, but may be porphyritic, containing larger mineral crystals in an otherwise fine-grained groundmas
Loebejuener porphyr poliert
QAPF diagram with rhyolite field highlighted
Rhyolite beach on Lake Superior
Aphanitic rhyolite
Obsidian
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Obsidian is a naturally occurring volcanic glass formed when lava extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock. Produced from felsic lava, obsidian is rich
Rhyolite
…Rhyolitic ash-flow tuffs are among the most voluminous of continental igneous rock formations. Rhyolitic tuff has been used extensively for construction. Obsidian, which is rhyolitic volcanic glass, has been used for tools from prehistoric times to the present day because it can be shaped to an extremely sharp…
Lipari Obsidienne
Polished snowflake obsidian, formed through the inclusion of cristobalite crystals
Glass Mountain, a large obsidian flow at Medicine Lake Volcano in California
Jumble of pumice and volcanic obsidian, Obsidian Dome, California