Rhyolite is a fine-grained igneous extrusive rock of high silica content or felsic rock. Rhyolite is composed principally of quartz and feldspar minerals, and traces of biotite, plagioclase, mica, amphibiotes, and pyroxenes. It resembles granite in mineral composition, although granite is an intrusive igneous rock. Rhyolite is of a glassy texture and its colors may vary from white to gray to light gray. Igneous extrusive rocks form with or without crystallization. Rhyolite usually forms after lava has been extruded from the underground and cooled by coming in contact with the atmosphere. Rhyolite lavas are highly viscous, and tend to explode when coming in contact with the air as they’re ejected from volcanoes.
Extrusive cooling
Extrusive cooling refers to the way in which igneous volcanic rocks are created. Igneous rock formed through extrusive cooling is first extruded to the surface as hot lava. When lava, due to its high viscosity and accumulated gases, reaches the surface, it explodes violently into the atmosphere, and falls as pyroclastic fragments back to the ground. Magma cools very rapidly once out in the air or when in contact with water, such as under the sea, with little crystallization. When a large portion of the magma fails to crystallize, it may become obsidian. If the lava contains high gas contents, then it becomes pumice, when its components are released as free gas.
How is rhyolite metamorphosed?
Below the surface of the Earth, there is molten rock known as magma. Magma is a mixture of various elements, including silica, sodium, potassium, iron, etc. as magma cools; these elements form crystalline chains in geometric patterns to create the eight igneous rock forming minerals. Some minerals become solid at high temperatures, while others will do the same at lower temperatures. If the process of cooling of magma is slow, taking thousands or perhaps millions of years, such as below the ground, the minerals recrystallize large enough to be seen with the naked eye. They are coarse grained, but if the cooling is rapid, such as in the ambient temperature on the Earth’s surface, the minerals usually do not crystalize and develop fine-grained igneous rocks, such as rhyolite.
How is it used?
Rhyolite is used as a decorative stone in the landscaping industry and in the fabrication of some jewelry and ornaments. Rhyolite can be seen in various jewelry designs, including necklaces, bracelets, among many others. In the road construction industry, rhyolite is often used as an aggregate to asphalt; however, for its high silica content, it is rarely used as a concrete aggregate. For its characteristics, rhyolite was used by Native American Indians to make tools, including scrapers, blades, and hammer stones, among others.
Where is rhyolite found?
Igneous rock does not occur anywhere, fractionation of igneous rocks most commonly occurs at the divergence and convergence of plate tectonics, where volcanoes are formed. Extrusive rocks often form when lava gets ejected to the surface and becomes a lava flow, or when it explodes dramatically into pyroclastic ejections into the sky. Rhyolite is created when highly viscous lava flow is cooled after coming in contact the air. Rhyolite is found in oceanic islands and rifted continental crusts. Rhyolite lavas are also found in continental and submarine volcanoes, especially island arcs, and in igneous dikes. Rhyolite is found in abundance in the Yellowstone Park area and throughout the southwestern portion of the United States, including Sierra County, New Mexico. It occurs in the Taupo volcanic zone in New Zealand as well.
Igneous rocks have played an important of the Earth’s evolution. The fractionation of igneous rocks most commonly occurs at the boundaries of plate tectonics in both the ocean floor and on land. The fractionation of igneous rocks is an important process for the geological changes occurring in the Earth. According to jmu.edu, the fractionation of igneous rocks has helped formed the volcanic arcs and continents of the world.
