Rhyolith

Part of speech: noun

Definitions

1. A fine-grained, light-colored volcanic rock rich in silica that forms when lava cools quickly at the earth's surface
2. An igneous stone of silica-rich volcanic origin, typically pale in color, produced when molten lava cools rapidly
3. Pale, fine-textured volcanic rock containing abundant silica, formed when viscous lava solidifies near the surface

Etymology: Rhyolite was named in 1860 by the German geologist Ferdinand von Richthofen, who coined it from the Greek "rhyax", meaning "stream of lava", and "lithos", meaning "stone". The name was chosen to describe the flowing, lava-like appearance he saw in these pale volcanic rocks, though the rock itself is usually light in colour because it is rich in silica. The word "rhyolith" is a variant spelling in the same family, but the standard English form is "rhyolite", which is the one used in geology texts. Both forms trace back to the same Greek elements, and the German coinage passed into English scientific writing in the later 19th century.