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42-437: Big Southern Butte consists of two coalesced lava domes with a base diameter of 6.5 kilometres (4.0 mi) and a combined volume of approximately 8 cubic kilometres (1.9 cu mi). This Butte County , Idaho state location article is a stub . You can help Misplaced Pages by expanding it . This volcanology article is a stub . You can help Misplaced Pages by expanding it . Lava dome In volcanology ,

84-525: A lava dome is a 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 form lava domes. 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

126-450: A cryptodome was in the May 1980 eruption of Mount St. Helens , where the explosive eruption began after a landslide caused the side of the volcano to collapse, leading to explosive decompression of the subterranean cryptodome. A lava spine or lava spire is a growth that can form on the top of a lava dome. A lava spine can increase the instability of the underlying lava dome. A recent example of

168-504: A flow front 400 metres (1,300 ft) tall (the dark scalloped line at lower left). There is another prominent coulée flow on the flank of Llullaillaco volcano, in Argentina , and other examples in the Andes . Silica Silicon dioxide , also known as silica , is an oxide of silicon with the chemical formula SiO 2 , commonly found in nature as quartz . In many parts of

210-407: A glass with no true melting point, can be used as a glass fibre for fibreglass. Silicon dioxide is mostly obtained by mining, including sand mining and purification of quartz . Quartz is suitable for many purposes, while chemical processing is required to make a purer or otherwise more suitable (e.g. more reactive or fine-grained) product. Precipitated silica or amorphous silica is produced by

252-494: A heat capacity minimum. Its density decreases from 2.08 g/cm at 1950 °C to 2.03 g/cm at 2200 °C. The molecular SiO 2 has a linear structure like CO 2 . It has been produced by combining silicon monoxide (SiO) with oxygen in an argon matrix. The dimeric silicon dioxide, (SiO 2 ) 2 has been obtained by reacting O 2 with matrix isolated dimeric silicon monoxide, (Si 2 O 2 ). In dimeric silicon dioxide there are two oxygen atoms bridging between

294-603: A lava spine is the spine formed in 1997 at the Soufrière Hills Volcano on Montserrat. Coulées (or coulees) are lava domes that have experienced some flow away from their original position, thus resembling both lava domes and lava flows . The world's largest known dacite flow is the Chao dacite dome complex , a huge coulée flow-dome between two volcanoes in northern Chile . This flow is over 14 kilometres (8.7 mi) long, has obvious flow features like pressure ridges, and

336-450: A low value of 140° in α-tridymite, up to 180° in β-tridymite. In α-quartz, the Si–O–Si angle is 144°. Alpha quartz is the most stable form of solid SiO 2 at room temperature. The high-temperature minerals, cristobalite and tridymite, have both lower densities and indices of refraction than quartz. The transformation from α-quartz to beta-quartz takes place abruptly at 573 °C. Since

378-448: A rough indicator of magma supply , but it shows no systematic relationship to the timing or characteristics of lava dome explosions. Gravitational collapse of a lava dome can produce a block and ash flow . A cryptodome (from the Greek κρυπτός , kryptos , "hidden, secret") is a dome-shaped structure created by accumulation of viscous magma at a shallow depth. One example of

420-410: A silicon wafer enables it to overcome the surface states that otherwise prevent electricity from reaching the semiconducting layer. The process of silicon surface passivation by thermal oxidation (silicon dioxide) is critical to the semiconductor industry . It is commonly used to manufacture metal–oxide–semiconductor field-effect transistors (MOSFETs) and silicon integrated circuit chips (with

462-477: A very shallow layer of about 1 nm or 10 Å of so-called native oxide. Higher temperatures and alternative environments are used to grow well-controlled layers of silicon dioxide on silicon, for example at temperatures between 600 and 1200 °C, using so-called dry oxidation with O 2 or wet oxidation with H 2 O. The native oxide layer is beneficial in microelectronics , where it acts as electric insulator with high chemical stability. It can protect

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504-524: A white powder with extremely low bulk density (0.03-0.15 g/cm ) and thus high surface area. The particles act as a thixotropic thickening agent, or as an anti-caking agent, and can be treated to make them hydrophilic or hydrophobic for either water or organic liquid applications. Silica fume is an ultrafine powder collected as a by-product of the silicon and ferrosilicon alloy production. It consists of amorphous (non-crystalline) spherical particles with an average particle diameter of 150 nm, without

546-435: Is a common fundamental constituent of glass . In the majority of silicon dioxides, the silicon atom shows tetrahedral coordination , with four oxygen atoms surrounding a central Si atom ( see 3-D Unit Cell ). Thus, SiO 2 forms 3-dimensional network solids in which each silicon atom is covalently bonded in a tetrahedral manner to 4 oxygen atoms. In contrast, CO 2 is a linear molecule. The starkly different structures of

588-439: Is also the primary component of rice husk ash , which is used, for example, in filtration and as supplementary cementitious material (SCM) in cement and concrete manufacturing. Silicification in and by cells has been common in the biological world and it occurs in bacteria, protists, plants, and animals (invertebrates and vertebrates). Prominent examples include: About 95% of the commercial use of silicon dioxide (sand)

630-486: 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

672-465: Is in the construction industry, e.g. in the production of concrete ( Portland cement concrete ). Certain deposits of silica sand, with desirable particle size and shape and desirable clay and other mineral content, were important for sand casting of metallic products. The high melting point of silica enables it to be used in such applications such as iron casting; modern sand casting sometimes uses other minerals for other reasons. Crystalline silica

714-651: Is obtained by the dealumination of a low-sodium, ultra-stable Y zeolite with combined acid and thermal treatment. The resulting product contains over 99% silica, and has high crystallinity and specific surface area (over 800 m /g). Faujasite-silica has very high thermal and acid stability. For example, it maintains a high degree of long-range molecular order or crystallinity even after boiling in concentrated hydrochloric acid . Molten silica exhibits several peculiar physical characteristics that are similar to those observed in liquid water : negative temperature expansion, density maximum at temperatures ~5000 °C, and

756-421: Is rapidly cooled, it does not crystallize, but solidifies as a glass. Because of this, most ceramic glazes have silica as the main ingredient. The structural geometry of silicon and oxygen in glass is similar to that in quartz and most other crystalline forms of silicon and oxygen, with silicon surrounded by regular tetrahedra of oxygen centres. The difference between the glass and crystalline forms arises from

798-426: Is the major constituent of sand . Even though it is poorly soluble, silica occurs in many plants such as rice . Plant materials with high silica phytolith content appear to be of importance to grazing animals, from chewing insects to ungulates . Silica accelerates tooth wear, and high levels of silica in plants frequently eaten by herbivores may have developed as a defense mechanism against predation. Silica

840-453: Is the only polymorph of silica stable at the Earth's surface. Metastable occurrences of the high-pressure forms coesite and stishovite have been found around impact structures and associated with eclogites formed during ultra-high-pressure metamorphism . The high-temperature forms of tridymite and cristobalite are known from silica-rich volcanic rocks . In many parts of the world, silica

882-504: Is the process by which a semiconductor surface is rendered inert, and does not change semiconductor properties as a result of interaction with air or other materials in contact with the surface or edge of the crystal. The formation of a thermally grown silicon dioxide layer greatly reduces the concentration of electronic states at the silicon surface . SiO 2 films preserve the electrical characteristics of p–n junctions and prevent these electrical characteristics from deteriorating by

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924-436: Is used as a fining agent for wine, beer, and juice, with the E number reference E551 . In cosmetics, silica is useful for its light-diffusing properties and natural absorbency. Diatomaceous earth , a mined product, has been used in food and cosmetics for centuries. It consists of the silica shells of microscopic diatoms ; in a less processed form it was sold as "tooth powder". Manufactured or mined hydrated silica

966-489: Is used as the hard abrasive in toothpaste . Silicon dioxide is widely used in the semiconductor technology: Because silicon dioxide is a native oxide of silicon it is more widely used compared to other semiconductors like gallium arsenide or indium phosphide . Silicon dioxide could be grown on a silicon semiconductor surface. Silicon oxide layers could protect silicon surfaces during diffusion processes , and could be used for diffusion masking. Surface passivation

1008-418: Is used in hydraulic fracturing of formations which contain tight oil and shale gas . Silica is the primary ingredient in the production of most glass . As other minerals are melted with silica, the principle of freezing point depression lowers the melting point of the mixture and increases fluidity. The glass transition temperature of pure SiO 2 is about 1475 K. When molten silicon dioxide SiO 2

1050-538: Is used to produce elemental silicon . The process involves carbothermic reduction in an electric arc furnace : Fumed silica , also known as pyrogenic silica, is prepared by burning SiCl 4 in an oxygen-rich hydrogen flame to produce a "smoke" of SiO 2 . It can also be produced by vaporizing quartz sand in a 3000 °C electric arc. Both processes result in microscopic droplets of amorphous silica fused into branched, chainlike, three-dimensional secondary particles which then agglomerate into tertiary particles,

1092-623: The Moon , Venus , and Mars , e.g. the Martian surface in the western part of Arcadia Planitia and within Terra Sirenum . Lava domes evolve unpredictably, due to non-linear dynamics caused by crystallization and outgassing of the highly viscous lava in the dome's conduit . Domes undergo various processes such as growth, collapse, solidification and erosion . Lava domes grow by endogenic dome growth or exogenic dome growth. The former implies

1134-550: The planar process ). Hydrophobic silica is used as a defoamer component . In its capacity as a refractory , it is useful in fiber form as a high-temperature thermal protection fabric. Silica is used in the extraction of DNA and RNA due to its ability to bind to the nucleic acids under the presence of chaotropes . Silica aerogel was used in the Stardust spacecraft to collect extraterrestrial particles. Pure silica (silicon dioxide), when cooled as fused quartz into

1176-496: The acidification of solutions of sodium silicate . The gelatinous precipitate or silica gel , is first washed and then dehydrated to produce colorless microporous silica. The idealized equation involving a trisilicate and sulfuric acid is: Approximately one billion kilograms/year (1999) of silica were produced in this manner, mainly for use for polymer composites – tires and shoe soles. Thin films of silica grow spontaneously on silicon wafers via thermal oxidation , producing

1218-552: The branching of the pyrogenic product. The main use is as pozzolanic material for high performance concrete. Fumed silica nanoparticles can be successfully used as an anti-aging agent in asphalt binders. Silica, either colloidal, precipitated, or pyrogenic fumed, is a common additive in food production. It is used primarily as a flow or anti- caking agent in powdered foods such as spices and non-dairy coffee creamer, or powders to be formed into pharmaceutical tablets. It can adsorb water in hygroscopic applications. Colloidal silica

1260-506: The connectivity of the tetrahedral units: Although there is no long-range periodicity in the glassy network, ordering remains at length scales well beyond the SiO bond length. One example of this ordering is the preference to form rings of 6-tetrahedra. The majority of optical fibers for telecommunications are also made from silica. It is a primary raw material for many ceramics such as earthenware , stoneware , and porcelain . Silicon dioxide

1302-488: The densest of the low-pressure forms, which has a density of 2.648 g/cm . The difference in density can be ascribed to the increase in coordination as the six shortest Si–O bond lengths in stishovite (four Si–O bond lengths of 176 pm and two others of 181 pm) are greater than the Si–O bond length (161 pm) in α-quartz. The change in the coordination increases the ionicity of the Si–O bond. Faujasite silica, another polymorph,

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1344-459: The dioxides of carbon and silicon are a manifestation of the double bond rule . Based on the crystal structural differences, silicon dioxide can be divided into two categories: crystalline and non-crystalline (amorphous). In crystalline form, this substance can be found naturally occurring as quartz , tridymite (high-temperature form), cristobalite (high-temperature form), stishovite (high-pressure form), and coesite (high-pressure form). On

1386-708: The enlargement of a lava dome due to the influx of magma into the dome interior, and the latter refers to discrete lobes of lava emplaced upon the surface of the dome. It is the high viscosity of the lava that prevents it from flowing far from the vent from which it extrudes, creating a dome-like shape of sticky lava that then cools slowly in-situ. Spines and lava flows are common extrusive products of lava domes. Domes may reach heights of several hundred meters, and can grow slowly and steadily for months (e.g. Unzen volcano), years (e.g. Soufrière Hills volcano), or even centuries (e.g. Mount Merapi volcano). The sides of these structures are composed of unstable rock debris. Due to

1428-411: The gaseous ambient environment. Silicon oxide layers could be used to electrically stabilize silicon surfaces. The surface passivation process is an important method of semiconductor device fabrication that involves coating a silicon wafer with an insulating layer of silicon oxide so that electricity could reliably penetrate to the conducting silicon below. Growing a layer of silicon dioxide on top of

1470-425: The intermittent buildup of gas pressure , erupting domes can often experience episodes of explosive eruption over time. If part of a lava dome collapses and exposes pressurized magma, pyroclastic flows can be produced. Other hazards associated with lava domes are the destruction of property from lava flows , forest fires , and lahars triggered from re-mobilization of loose ash and debris. Lava domes are one of

1512-400: The other hand, amorphous silica can be found in nature as opal and diatomaceous earth . Quartz glass is a form of intermediate state between these structures. All of these distinct crystalline forms always have the same local structure around Si and O. In α-quartz the Si–O bond length is 161 pm, whereas in α-tridymite it is in the range 154–171 pm. The Si–O–Si angle also varies between

1554-567: The principal structural features of many stratovolcanoes worldwide. Lava domes are prone to unusually dangerous explosions since they can contain rhyolitic silica -rich lava. Characteristics of lava dome eruptions include shallow, long-period and hybrid seismicity , which is attributed to excess fluid pressures in the contributing vent chamber. Other characteristics of lava domes include their hemispherical dome shape, cycles of dome growth over long periods, and sudden onsets of violent explosive activity. The average rate of dome growth may be used as

1596-401: The silicon atoms with an Si–O–Si angle of 94° and bond length of 164.6 pm and the terminal Si–O bond length is 150.2 pm. The Si–O bond length is 148.3 pm, which compares with the length of 161 pm in α-quartz. The bond energy is estimated at 621.7 kJ/mol. SiO 2 is most commonly encountered in nature as quartz , which comprises more than 10% by mass of the Earth's crust. Quartz

1638-418: The silicon, store charge, block current, and even act as a controlled pathway to limit current flow. Many routes to silicon dioxide start with an organosilicon compound, e.g., HMDSO, TEOS. Synthesis of silica is illustrated below using tetraethyl orthosilicate (TEOS). Simply heating TEOS at 680–730 °C results in the oxide: Similarly TEOS combusts around 400 °C: TEOS undergoes hydrolysis via

1680-492: The so-called sol-gel process . The course of the reaction and nature of the product are affected by catalysts, but the idealized equation is: Being highly stable, silicon dioxide arises from many methods. Conceptually simple, but of little practical value, combustion of silane gives silicon dioxide. This reaction is analogous to the combustion of methane: However the chemical vapor deposition of silicon dioxide onto crystal surface from silane had been used using nitrogen as

1722-446: The transformation is accompanied by a significant change in volume, it can easily induce fracturing of ceramics or rocks passing through this temperature limit. The high-pressure minerals, seifertite , stishovite, and coesite, though, have higher densities and indices of refraction than quartz. Stishovite has a rutile -like structure where silicon is 6-coordinate. The density of stishovite is 4.287 g/cm , which compares to α-quartz,

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1764-482: The world, silica is the major constituent of sand . Silica is one of the most complex and abundant families of materials , existing as a compound of several minerals and as a synthetic product. Examples include fused quartz , fumed silica , opal , and aerogels . It is used in structural materials , microelectronics , and as components in the food and pharmaceutical industries. All forms are white or colorless, although impure samples can be colored. Silicon dioxide

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