RHYOLITE - An extrusive igneous rock equivalent in composition to granite, in which the crystalline constituents are too small to be distinguished with the unaided eye.
Rhyolite is a type of volcanic rock, not a mineral, but usually with many minerals in it. It's like granite but forms on the surface of the Earth from fast-cooled magma, while granite is formed underground. Here are its main features:
Composition: Rhyolite is very rich in silica (silica content exceeds 70%) and usually contains much quartz, feldspar (both plagioclase and alkali feldspar), and either biotite or hornblende. Because it contains these minerals, rhyolite is colored light: most commonly white, pink, or gray.
Texture: Rhyolite may have numerous textures because of the differing ways that lava can be cooled. Most commonly it is glassy (just like obsidian), aphanitic, or porphyritic with large crystals in a fine-grained or glassy matrix.
Formation: Rhyolite is formed from thick lava because it contains a lot of silica. This type of lava can cause explosive volcanic eruptions and is associated with volcanic domes, calderas, and ash-flow tuffs.
Uses: Rhyolite is not commonly used in industry, but it may be used as crushed stone for building or as decorative rock. Its minerals also help scientists study geological processes.
Rhyolite occurs where there is volcanic activity, such as Yellowstone National Park, Iceland, and parts of the southwestern United States. It typically results from volcanism of continental areas or subduction zones.
Despite its similar name, Rhyolite the rock should not be confused with the town of Rhyolite, Nevada. The town was named because this rock is found in the area.
By Michael C. Rygel - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=31125057
