Rhyolite (/ˈraɪ.ə.laɪt, ˈraɪ.oʊ-/ RY-ə-lyte, RY-oh-) is an igneous, volcanic rock, of felsic (silica-rich) composition (typically > 69% SiO2 – see the TAS classification). It may have any texture from glassy to aphanitic to porphyritic. The mineral assemblage is usually quartz, sanidine and plagioclase (in a ratio > 2:1 – see the QAPF diagram). Biotite and hornblende are common accessory minerals. It is the extrusive equivalent to granite.
|Felsic: igneous quartz and alkali feldspar (sanidine and sodic plagioclase), biotite and hornblende|
Rhyolite can be considered as the extrusive equivalent to the plutonic granite rock, and consequently, outcrops of rhyolite may bear a resemblance to granite. Due to their high content of silica and low iron and magnesium contents, rhyolitic magmas form highly viscous lavas. They also occur as breccias or in volcanic plugs and dikes. Rhyolites that cool too quickly to grow crystals form a natural glass or vitrophyre, also called obsidian. Slower cooling forms microscopic crystals in the lava and results in textures such as flow foliations, spherulitic, nodular, and lithophysal structures. Some rhyolite is highly vesicular pumice. Many eruptions of rhyolite are highly explosive and the deposits may consist of fallout tephra/tuff or of ignimbrites.
Eruptions of rhyolite are relatively rare compared to eruptions of less felsic lavas. Only three eruptions of rhyolite have been recorded since the start of the 20th century: at the St. Andrew Strait volcano in Papua New Guinea, Novarupta volcano in Alaska, and Chaiten in southern Chile.
Rhyolite has been found on islands far from land, but such oceanic occurrences are rare.
The name rhyolite was introduced into geology in 1860 by the German traveler and geologist Ferdinand von Richthofen from the Greek word rhýax ("a stream of lava") and the rock name suffix "-lite".
In North American pre-historic times, rhyolite was quarried extensively in eastern Pennsylvania in the United States. Among the leading quarries was the Carbaugh Run Rhyolite Quarry Site in Adams County. Rhyolite was mined there starting 11,500 years ago. Tons of rhyolite were traded across the Delmarva Peninsula, because the rhyolite kept a sharp point when knapped and was used to make spear points and arrowheads.
Alunite is a hydrated aluminium potassium sulfate mineral, formula KAl3(SO4)2(OH)6. It was first observed in the 15th century at Tolfa, near Rome, where it is mined for the manufacture of alum. First called aluminilite by J.C. Delamétherie in 1797, this name was contracted by François Beudant three decades later to alunite.
Alunite crystals morphologically are rhombohedra with interfacial angles of 90° 50', causing them to resemble cubes. Crystal symmetry is trigonal. Minute glistening crystals have also been found loose in cavities in altered rhyolite. Alunite varies in color from white to yellow gray. The hardness is 4 and the specific gravity is between 2.6 and 2.8. It is insoluble in water or weak acids, but soluble in sulfuric acid.
Sodium can substitute for potassium in the mineral, and when the sodium content is high, is called natroalunite.
Alunite is an analog of Jarosite, where aluminium replaces Fe3+. Alunite occurs as a secondary mineral on iron sulfate ores.
Alunite occurs as veins and replacement masses in trachyte, rhyolite, and similar potassium rich volcanic rocks. It is formed by the action of sulfuric acid bearing solutions on these rocks during the oxidation and leaching of metal sulfide deposits. Alunite also is found near volcanic fumaroles. The white, finely granular masses closely resemble finely granular limestone, dolomite, anhydrite, and magnesite in appearance. The more compact kinds from Hungary are so hard and tough that they have been used for millstones.Historically extensive deposits were mined in Tuscany and Hungary, and at Bulahdelah, New South Wales, Australia. It is currently mined at Tolfa, Italy. In the United States it is found in the San Juan district of Colorado; Goldfield, Nevada; the ghost town of Alunite, Utah near Marysvale; and Red Mountain near Patagonia, Arizona. The Arizona occurrence lies appropriately above a canyon named Alum Gulch. Alunite is mined as an ore of both potassium and aluminium at Marysvale. Some of the ore deposits were located by airborne and satellite multispectral imaging.
An article in the May/June 2019 issue of Archaeology magazine states that in China, in Henan province, an assortment of ceramic objects and jars were found, dating back 2000 years. In one of the jars, a mixture of alunite and potassium nitrate was found. The mixture was then thought to be a "mixture of immortality" mentioned in ancient Chinese texts. Obviously, this does not appear to have succeeded.Aquacade (satellite)
Aquacade, previously designated Rhyolite, was a class of SIGINT spy satellites operated by the National Reconnaissance Office for the United States Central Intelligence Agency. The National Security Agency (NSA) was also reportedly involved. The program, also known by SIGAD AFP-720 and SIGAD AFP-472, respectively, is still classified. During the same period, the Canyon SIGINT satellites were in use with an apparently somewhat different set of capabilities.
The name of the program, originally "Rhyolite", was changed to "Aquacade" in 1975 following the disclosure of the codeword "Rhyolite" in the trial of Christopher Boyce and Andrew Lee.
The Rhyolite/Aquacade satellites, made by TRW, are rumored to have an umbrella-like reflecting dish 20 meters in diameter. They were succeeded by the Magnum/Orion and Mentor series of satellites.
A major purpose of the Rhyolite satellites was reportedly the interception of Soviet and Chinese microwave relay signals traffic. During the 1960s-1970s, much of the long distance telephone and data traffic in both the US and Eastern Europe was carried by terrestrial microwave relay links, each consisting of a dish antenna on a microwave tower that transmitted a narrow beam of microwaves to a receiving dish in a nearby city. A good deal of the microwave beam would miss the receiving dish and, because of the curvature of the Earth, radiate out into space. By placing a satellite in a geosynchronous orbit at a position in the sky where it could intercept the beam, the US government was able to listen in on Soviet telephone calls and telex cables during the Cold War.Beatty, Nevada
Beatty (pronounced BAY-dee) is an unincorporated town along the Amargosa River in Nye County in the U.S. state of Nevada. U.S. Route 95 runs through the town, which lies between Tonopah, about 90 miles (140 km) to the north, and Las Vegas, about 120 miles (190 km) to the southeast. State Route 374 connects Beatty to Death Valley National Park, about 8 miles (13 km) to the west.
Before the arrival of non-indigenous people in the 19th century, the region was home to groups of Western Shoshone. Established in 1905, the community was named after Montillus (Montillion) Murray "Old Man" Beatty, who settled on a ranch in the Oasis Valley in 1896 and became Beatty's first postmaster. With the arrival of the Las Vegas and Tonopah Railroad in 1905, the town became a railway center for the Bullfrog Mining District, including mining towns such as nearby Rhyolite. Starting in the 1940s, Nellis Air Force Base and other federal installations contributed to the town's economy as did tourism related to Death Valley National Park and the rise of Las Vegas as an entertainment center.
Beatty is home to the Beatty Museum and Historical Society and to businesses catering to tourist travel. The ghost town of Rhyolite and the Goldwell Open Air Museum (a sculpture park), are both about 4 miles (6 km) to the west, and Yucca Mountain and the Nevada Test Site are about 18 miles (29 km) to the east.Calc-alkaline magma series
The calc-alkaline magma series is one of two main subdivisions of the subalkaline magma series, the other subalkaline magma series being the tholeiitic. A magma series is a series of compositions that describes the evolution of a mafic magma, which is high in magnesium and iron and produces basalt or gabbro, as it fractionally crystallizes to become a felsic magma, which is low in magnesium and iron and produces rhyolite or granite. Calc-alkaline rocks are rich in alkaline earths (magnesia and calcium oxide) and alkali metals and make up a major part of the crust of the continents.
The diverse rock types in the calc-alkaline series include volcanic types such as basalt, andesite, dacite, rhyolite, and also their coarser-grained intrusive equivalents (gabbro, diorite, granodiorite, and granite). They do not include silica-undersaturated, alkalic, or peralkaline rocks.Dacite
Dacite ( ) is an igneous, volcanic rock. It has an aphanitic to porphyritic texture and is intermediate in composition between andesite and rhyolite. The word dacite comes from Dacia, a province of the Roman Empire which lay between the Danube River and Carpathian Mountains (now modern Romania and Moldova) where the rock was first described.Extrusive rock
Extrusive rock refers to the mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava or explodes violently into the atmosphere to fall back as pyroclastics or tuff. This is as opposed to intrusive rock formation, in which magma does not reach the surface.The main effect of extrusion is that the magma can cool much more quickly in the open air or under seawater, and there is little time for the growth of crystals. Sometimes, a residual portion of the matrix fails to crystallize at all, instead becoming a natural glass or obsidian.
If the magma contains abundant volatile components which are released as free gas, then it may cool with large or small vesicles (bubble-shaped cavities) such as in pumice, scoria, or vesicular basalt. Examples of extrusive rocks include basalt, rhyolite, andesite, obsidian and pumice, scoria, and feldspar.Felsic
In geology, felsic refers to igneous rocks that are relatively rich in elements that form feldspar and quartz. It is contrasted with mafic rocks, which are relatively richer in magnesium and iron. Felsic refers to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. Felsic magma or lava is higher in viscosity than mafic magma/lava.
Felsic rocks are usually light in color and have specific gravities less than 3. The most common felsic rock is granite. Common felsic minerals include quartz, muscovite, orthoclase, and the sodium-rich plagioclase feldspars (albite-rich).Felsite
Felsite is a very fine-grained volcanic rock that may or may not contain larger crystals. Felsite is a field term for a light-colored rock that typically requires petrographic examination or chemical analysis for more precise definition. Color is generally white through light gray, or red to tan and may include any color except dark gray, green or black (the colors of trap rock). The mass of the rock consists of a fine-grained matrix of felsic materials, particularly quartz, sodium and potassium feldspar, and may be termed a quartz felsite or quartz porphyry if the quartz phenocrysts are present. This rock is typically of extrusive origin, formed by compaction of fine volcanic ash, and may be found in association with obsidian and rhyolite. In some cases, it is sufficiently fine-grained for use in making stone tools. Its fine texture and felsic components allow for good knapped pieces, much like working chert, producing conchoidal fracture.
Dendritic manganese oxides such as pyrolusite and/or iron oxides such as limonite may precipitate along rock crevices, giving some rock chunk surfaces multicolored or arborescent patterned textures.Geology of Jersey
The geology of Jersey is characterised by the Late Proterozoic Brioverian volcanics, the Cadomian Orogeny, and only small signs of later deposits from the Cambrian and Quaternary periods. The kind of rocks go from conglomerate to shale, volcanic, intrusive and plutonic igneous rocks of many compositions, and metamorphic rocks as well, thus including most major types.Glass House Mountains National Park
Glass House Mountains National Park is a heritage-listed national park at Glass House Mountains, Sunshine Coast Region, Queensland, Australia. It is also known as Beerburrum Forest Reserve 1. It is 70 km (43 mi) north of Brisbane and consists of a flat plain punctuated by rhyolite and trachyte volcanic plugs, the cores of extinct volcanoes that formed 27 million to 26 million years ago. The mountains would once have had pyroclastic exteriors, but these have eroded away.
The national park was established in 1994. On 23 June 2010 the Queensland Government announced the expansion of the park to include an additional 2,117 hectares (5,230 acres). It was added to the Queensland Heritage Register on 3 May 2007.Ground stone
In archaeology, ground stone is a category of stone tool formed by the grinding of a coarse-grained tool stone, either purposely or incidentally. Ground stone tools are usually made of basalt, rhyolite, granite, or other cryptocrystalline and igneous stones whose coarse structure makes them ideal for grinding other materials, including plants and other stones.Lava dome
In volcanology, a lava dome or volcanic dome is a roughly circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano. Dome-building eruptions are common, particularly in convergent plate boundary settings. Around 6% of eruptions on earth are lava dome forming. The geochemistry of lava domes can vary from basalt (e.g. Semeru, 1946) to rhyolite (e.g. Chaiten, 2010) although the majority are of intermediate composition (such as Santiaguito, dacite-andesite, present day) The characteristic dome shape is attributed to high viscosity that prevents the lava from flowing very far. This high viscosity can be obtained in two ways: by high levels of silica in the magma, or by degassing of fluid magma. Since viscous basaltic and andesitic domes weather fast and easily break apart by further input of fluid lava, most of the preserved domes have high silica content and consist of rhyolite or dacite.
Existence of lava domes has been suggested for some domed structures on the Moon, Venus, and Mars, e.g. the Martian surface in the western part of Arcadia Planitia and within Terra Sirenum.List of rock types
The following is a list of rock types recognized by geologists. There is no agreed number of specific types of rocks. Any unique combination of chemical composition, mineralogy, grain size, texture, or other distinguishing characteristics can describe a rock type. Additionally, different classification systems exist for each major type of rock. There are three major types of rock: igneous rock, metamorphic rock, and sedimentary rock.Mount Kineo
Mount Kineo is a prominent geological feature located on a 1,150-acre (470 ha) peninsula that extends from the easterly shore of Moosehead Lake in the northern forest of Maine. With 700-foot (210 m) cliffs rising straight up from the water, it is the central feature of Mount Kineo State Park, a protected area of 800 acres (320 ha) managed by the Maine Department of Agriculture, Conservation and Forestry.Rhyodacite
Rhyodacite is an extrusive volcanic rock intermediate in composition between dacite and rhyolite. It is the extrusive equivalent of granodiorite. Phenocrysts of sodium-rich plagioclase, sanidine, quartz, and biotite or hornblende are typically set in an aphanitic to glassy light to intermediate-colored matrix.
Rhyodacite is a high silica rock containing 20% to 60% quartz with the remaining constituents being mostly feldspar. The feldspar is a mix of alkaline feldspar and plagioclase, with plagioclase forming 35% to 65% of the mix.
Rhyodacite often exists as explosive pyroclastic volcanic deposits.
Rhyodacite lava flows occur, for example, in northwestern Ferry County (Washington), and at An Sgùrr on the island of Eigg in Scotland.Rhyolite, Nevada
Rhyolite is a ghost town in Nye County, in the U.S. state of Nevada. It is in the Bullfrog Hills, about 120 miles (190 km) northwest of Las Vegas, near the eastern edge of Death Valley. The town began in early 1905 as one of several mining camps that sprang up after a prospecting discovery in the surrounding hills. During an ensuing gold rush, thousands of gold-seekers, developers, miners and service providers flocked to the Bullfrog Mining District. Many settled in Rhyolite, which lay in a sheltered desert basin near the region's biggest producer, the Montgomery Shoshone Mine.
Industrialist Charles M. Schwab bought the Montgomery Shoshone Mine in 1906 and invested heavily in infrastructure, including piped water, electric lines and railroad transportation, that served the town as well as the mine. By 1907, Rhyolite had electric lights, water mains, telephones, newspapers, a hospital, a school, an opera house, and a stock exchange. Published estimates of the town's peak population vary widely, but scholarly sources generally place it in a range between 3,500 and 5,000 in 1907–08.
Rhyolite declined almost as rapidly as it rose. After the richest ore was exhausted, production fell. The 1906 San Francisco earthquake and the financial panic of 1907 made it more difficult to raise development capital. In 1908, investors in the Montgomery Shoshone Mine, concerned that it was overvalued, ordered an independent study. When the study's findings proved unfavorable, the company's stock value crashed, further restricting funding. By the end of 1910, the mine was operating at a loss, and it closed in 1911. By this time, many out-of-work miners had moved elsewhere, and Rhyolite's population dropped well below 1,000. By 1920, it was close to zero.
After 1920, Rhyolite and its ruins became a tourist attraction and a setting for motion pictures. Most of its buildings crumbled, were salvaged for building materials, or were moved to nearby Beatty or other towns, although the railway depot and a house made chiefly of empty bottles were repaired and preserved. From 1988 to 1998, three companies operated a profitable open-pit mine at the base of Ladd Mountain, about 1 mile (1.6 km) south of Rhyolite. The Goldwell Open Air Museum lies on private property just south of the ghost town, which is on property overseen by the Bureau of Land Management.Tool stone
In archaeology, a tool stone is a type of stone that is used to manufacture stone tools,
or stones used as the raw material for tools.Generally speaking, tools that require a sharp edge are made using cryptocrystalline materials that fracture in an easily controlled conchoidal manner.
Cryptocrystalline tool stones include flint and chert, which are fine-grained sedimentary materials; rhyolite and felsite, which are igneous flowstones; and obsidian, a form of natural glass created by igneous processes. These materials fracture in a predictable fashion, and are easily resharpened. For more information on this subject, see lithic reduction.
Large-grained materials, such as basalt, granite, and sandstone, may also be used as tool stones, but for a very different purpose: they are ideal for ground stone artifacts. Whereas cryptocrystalline materials are most useful for killing and processing animals, large-grained materials are usually used for processing plant matter. Their rough faces often make excellent surfaces for grinding plant seeds. With much effort, some large-grained stones may be ground down into awls, adzes, and axes.Tuff
Tuff (from the Italian tufo), also known as volcanic tuff, is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is compacted into a solid rock in a process called consolidation. Tuff is sometimes erroneously called "tufa", particularly when used as construction material, but properly speaking, tufa is a limestone precipitated from groundwater. Rock that contains greater than 50% tuff is considered tuffaceous.
Tuff is a relatively soft rock, so it has been used for construction since ancient times. Since it is common in Italy, the Romans used it often for construction. The Rapa Nui people used it to make most of the moai statues in Easter Island.
Tuff can be classified as either sedimentary or igneous rock. They are usually studied in the context of igneous petrology, although they are sometimes described using sedimentological terms.Tweed Volcano
Tweed Volcano is a partially eroded Early Miocene shield volcano located in northeastern New South Wales, which formed when this region of Australia passed over the East Australia hotspot around 23 million years ago. Mount Warning, Lamington Plateau and the Border Ranges between New South Wales and Queensland are among the remnants of this volcano that was originally over 100 kilometres (62 mi) in diameter and nearly twice the height of Mount Warning today, at 1,156 metres (3,793 ft). Despite its size, Tweed Volcano was not a supervolcano; other shield volcanoes - such as on Hawaii - are much larger. In the 23 million years since the volcano was active, erosion has been extensive, forming a large erosion caldera around the volcanic plug of Mount Warning. Its erosion caldera is the largest in the Southern Hemisphere.
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