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85-548: It is a pegmatite geologic province which can be divided into the following megastructures: Middle Prydniprovia , Western Pryazovia , Eastern Pryazovia, Ingulski , Rosynsko- Tikychki , Dnistersko - Buzki and Volyn , which differ in mineralogical composition and geochemical specialization. The Ukrainian Shield and the Voronezh Massif consist of 3.2-3.8 Ga Archean crust in the southwest and east, and 2.3-2.1 Ga Early Proterozoic orogenic belts . The Ilyinets crater

170-420: A completely crystalline rock. Granitic rocks mainly consist of feldspar , quartz , mica , and amphibole minerals , which form an interlocking, somewhat equigranular matrix of feldspar and quartz with scattered darker biotite mica and amphibole (often hornblende ) peppering the lighter color minerals. Occasionally some individual crystals ( phenocrysts ) are larger than the groundmass , in which case

255-559: A pegmatitic gabbro ) is a coarse-grained rock containing patches of much coarser-grained rock of essentially the same composition. Individual crystals in pegmatites can be enormous in size. It is likely that the largest crystals ever found were feldspar crystals in pegmatites from Karelia with masses of thousands of tons. Quartz crystals with masses measured in thousands of pounds and micas over 10 meters (33 ft) across and 4 meters (13 ft) thick have been found. Spodumene crystals over 12 meters (40 ft) long have been found in

340-553: A basaltic magma to a granitic magma, but the quantities produced are small. For example, granitic rock makes up just 4% of the exposures in the South Sandwich Islands . In continental arc settings, granitic rocks are the most common plutonic rocks, and batholiths composed of these rock types extend the entire length of the arc. There are no indication of magma chambers where basaltic magmas differentiate into granites, or of cumulates produced by mafic crystals settling out of

425-412: A composition similar to granite , so that their most common minerals are quartz , feldspar , and mica . However, other pegmatite compositions are known, including compositions similar to nepheline syenite or gabbro . The term pegmatite is thus purely a textural description. Geologists typically prefix the term with a compositional description, so that granitic pegmatite is a pegmatite with

510-520: A diapir it would expend far too much energy in heating wall rocks, thus cooling and solidifying before reaching higher levels within the crust. Fracture propagation is the mechanism preferred by many geologists as it largely eliminates the major problems of moving a huge mass of magma through cold brittle crust. Magma rises instead in small channels along self-propagating dykes which form along new or pre-existing fracture or fault systems and networks of active shear zones. As these narrow conduits open,

595-509: A few (known as leucogranites ) contain almost no dark minerals. Granite is nearly always massive (lacking any internal structures), hard (falling between 6 and 7 on the Mohs hardness scale) , and tough. These properties have made granite a widespread construction stone throughout human history. The word "granite" comes from the Latin granum , a grain, in reference to the coarse-grained structure of such

680-450: A few pegmatites have a complex composition, with numerous unusual minerals of rare elements. These complex pegmatites are mined for lithium , beryllium , boron , fluorine , tin , tantalum , niobium , rare earth elements , uranium , and other valuable commodities. The word pegmatite derives from Homeric Greek , πήγνυμι ( pēgnymi ), which means “to bind together”, in reference to the intertwined crystals of quartz and feldspar in

765-610: A granite that is derived from partial melting of metasedimentary rocks may have more alkali feldspar, whereas a granite derived from partial melting of metaigneous rocks may be richer in plagioclase. It is on this basis that the modern "alphabet" classification schemes are based. The letter-based Chappell & White classification system was proposed initially to divide granites into I-type (igneous source) granite and S-type (sedimentary sources). Both types are produced by partial melting of crustal rocks, either metaigneous rocks or metasedimentary rocks. I-type granites are characterized by

850-565: A high content of sodium and calcium, and by a strontium isotope ratio, Sr/ Sr, of less than 0.708. Sr is produced by radioactive decay of Rb, and since rubidium is concentrated in the crust relative to the mantle, a low ratio suggests origin in the mantle. The elevated sodium and calcium favor crystallization of hornblende rather than biotite. I-type granites are known for their porphyry copper deposits. I-type granites are orogenic (associated with mountain building) and usually metaluminous. S-type granites are sodium-poor and aluminum-rich. As

935-611: A higher aluminium content (peraluminous granites). Intermediate pegmatites (NYF + LCT pegmatites) are known and may have formed by contamination of an initially NYF magma body with melted undepleted supracrustral rock. Pegmatites often contain rare elements and gemstones . Examples include aquamarine , tourmaline, topaz, fluorite, apatite, and corundum , often along with tin , rare earth, and tungsten minerals, among others. Pegmatites have been mined for both quartz and feldspar. For quartz mining, pegmatites with central quartz masses have been of particular interest. Pegmatites are

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1020-721: A larger intrusion. Pegmatites in low-grade metamorphic rock tend to be dominated by quartz and carbonate minerals . Pegmatites in metamorphic rock of higher grade are dominted by alkali feldspar . Gabbroic pegmatites typically occur as lenses within bodies of gabbro or diabase . Nepheline syenite pegmatites are common in alkaline igneous complexes. Volcanic rocks : Subvolcanic rocks : Plutonic rocks : Picrite basalt Peridotite Basalt Diabase (Dolerite) Gabbro Andesite Microdiorite Diorite Dacite Microgranodiorite Granodiorite Rhyolite Microgranite Granite Granite Granite ( / ˈ ɡ r æ n ɪ t / GRAN -it )

1105-820: A much higher proportion of clay with the Cecil soil series a prime example of the consequent Ultisol great soil group. Granite is a natural source of radiation , like most natural stones. Potassium-40 is a radioactive isotope of weak emission, and a constituent of alkali feldspar , which in turn is a common component of granitic rocks, more abundant in alkali feldspar granite and syenites . Some granites contain around 10 to 20 parts per million (ppm) of uranium . By contrast, more mafic rocks, such as tonalite, gabbro and diorite , have 1 to 5 ppm uranium, and limestones and sedimentary rocks usually have equally low amounts. Many large granite plutons are sources for palaeochannel -hosted or roll front uranium ore deposits , where

1190-536: A peculiar mineralogy and geochemistry, with particularly high silicon and potassium at the expense of calcium and magnesium and a high content of high field strength cations (cations with a small radius and high electrical charge, such as zirconium , niobium , tantalum , and rare earth elements .) They are not orogenic, forming instead over hot spots and continental rifting, and are metaluminous to mildly peralkaline and iron-rich. These granites are produced by partial melting of refractory lithology such as granulites in

1275-568: A range of hills, formed by the metamorphic aureole or hornfels . Granite often occurs as relatively small, less than 100 km stock masses ( stocks ) and in batholiths that are often associated with orogenic mountain ranges. Small dikes of granitic composition called aplites are often associated with the margins of granitic intrusions . In some locations, very coarse-grained pegmatite masses occur with granite. Granite forms from silica-rich ( felsic ) magmas. Felsic magmas are thought to form by addition of heat or water vapor to rock of

1360-449: A rate ranging from 1 m to 10 m per day. Pegmatites are the last part of a magma body to crystallize. This final fluid fraction is enriched in volatile and trace elements. The residual magma undergoes phase separation into a melt phase and a hydrous fluid phase saturated with silica , alkalis , and other elements. Such phase separation requires formation from a wet magma, rich enough in water to saturate before more than two-thirds of

1445-415: A result, they contain micas such as biotite and muscovite instead of hornblende. Their strontium isotope ratio is typically greater than 0.708, suggesting a crustal origin. They also commonly contain xenoliths of metamorphosed sedimentary rock, and host tin ores. Their magmas are water-rich, and they readily solidify as the water outgasses from the magma at lower pressure, so they less commonly make it to

1530-1042: A simple composition, often being composed entirely of minerals common in granite, such as feldspar, mica, and quartz. The feldspar and quartz often show graphic texture . Rarely, pegmatites are extremely enriched in incompatible elements , such as lithium , caesium , beryllium , tin , niobium , zirconium , uranium , thorium , boron, phosphorus, and fluorine. These complex pegmatites contain unusual minerals of these elements, such as beryl, spodumene, lepidolite, amblygonite, topaz, apatite, fluorite, tourmaline, triphylite , columbite , monazite , and molybdenite . Some of these can be important ore minerals. Some gemstones , such as emerald , are found almost exclusively in pegmatites. Nepheline syenite pegmatites typically contain zirconium, titanium , and rare earth element minerals. Gabbroic pegmatites typically consist of exceptionally coarse interlocking pyroxene and plagioclase . Pegmatites are enriched in volatile and incompatible elements , consistent with their likely origin as

1615-626: A very coarse texture , with large interlocking crystals usually greater in size than 1 cm (0.4 in) and sometimes greater than 1 meter (3 ft). Most pegmatites are composed of quartz , feldspar , and mica , having a similar silicic composition to granite . However, rarer intermediate composition and mafic pegmatites are known. Many of the world's largest crystals are found within pegmatites. These include crystals of microcline , quartz , mica , spodumene , beryl , and tourmaline . Some individual crystals are over 10 m (33 ft) long. Most pegmatites are thought to form from

1700-466: Is grus , which is often made up of coarse-grained fragments of disintegrated granite. Climatic variations also influence the weathering rate of granites. For about two thousand years, the relief engravings on Cleopatra's Needle obelisk had survived the arid conditions of its origin before its transfer to London. Within two hundred years, the red granite has drastically deteriorated in the damp and polluted air there. Soil development on granite reflects

1785-539: Is microgranite . The extrusive igneous rock equivalent of granite is rhyolite . Granitic rock is widely distributed throughout the continental crust . Much of it was intruded during the Precambrian age; it is the most abundant basement rock that underlies the relatively thin sedimentary veneer of the continents. Outcrops of granite tend to form tors , domes or bornhardts , and rounded massifs . Granites sometimes occur in circular depressions surrounded by

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1870-517: Is 3–6·10 Pa·s. The melting temperature of dry granite at ambient pressure is 1215–1260 °C (2219–2300 °F); it is strongly reduced in the presence of water, down to 650 °C at a few hundred megapascals of pressure. Granite has poor primary permeability overall, but strong secondary permeability through cracks and fractures if they are present. A worldwide average of the chemical composition of granite, by weight percent, based on 2485 analyses: The medium-grained equivalent of granite

1955-518: Is Wise's (2022) pegmatite classification, which focuses mostly on the source of the magma from which the pegmatite crystalizes. Pegmatites form under conditions in which the rate of new crystal nucleation is much slower than the rate of crystal growth . Large crystals are favored. In normal igneous rocks, coarse texture is a result of slow cooling deep underground. It is not clear if pegmatite forms by slow or rapid cooling. In some studies, crystals in pegmatitic conditions have been recorded to grow at

2040-850: Is a chilled margin whose composition is representative of the original melt. Pegmatites derived from batholiths can be divided into a family of NYF pegmatites, characterized by progressive enrichment in niobium , yttrium , and fluorine as well as enrichment in beryllium, rare earth elements, scandium , titanium, zirconium, thorium, and uranium; and a family of LCT pegmatites, characterized by progressive accumulation of lithium, caesium , and tantalum, as well as enrichment in rubidium , beryllium, tin, barium, phosphorus, and fluorine. The NYF pegmatites likely fractionated from A- to I-type granites that were relatively low in aluminium (subaluminous to metaluminous granites). These granites originated from depleted crust or mantle rock. LCT pegmatites most likely formed from S-type granites or possibly I-type granites, with

2125-480: Is a coarse-grained ( phaneritic ) intrusive igneous rock composed mostly of quartz , alkali feldspar , and plagioclase . It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies underground. It is common in the continental crust of Earth, where it is found in igneous intrusions . These range in size from dikes only a few centimeters across to batholiths exposed over hundreds of square kilometers. Granite

2210-410: Is an excess of aluminum beyond what can be taken up in feldspars (Al 2 O 3 > CaO + K 2 O + Na 2 O) are described as peraluminous , and they contain aluminum-rich minerals such as muscovite . The average density of granite is between 2.65 and 2.75 g/cm (165 and 172 lb/cu ft), its compressive strength usually lies above 200 MPa (29,000 psi), and its viscosity near STP

2295-618: Is believed to have a mass of around 81 tonnes. It was the tallest temple in south India. Imperial Roman granite was quarried mainly in Egypt, and also in Turkey, and on the islands of Elba and Giglio . Granite became "an integral part of the Roman language of monumental architecture". The quarrying ceased around the third century AD. Beginning in Late Antiquity the granite was reused, which since at least

2380-427: Is broad agreement on the basic mechanisms by which they form, the details of pegmatite formation remain enigmatic. Pegmatites have characteristics inconsistent with other igneous intrusions. They are not porphyritic , and show no chilled margin . On the contrary, the largest crystals are often found on the margins of the pegmatite body. While aplites are sometimes found on the margins, they are as likely to occur within

2465-434: Is called a binary or two-mica granite. Two-mica granites are typically high in potassium and low in plagioclase, and are usually S-type granites or A-type granites, as described below . Another aspect of granite classification is the ratios of metals that potentially form feldspars. Most granites have a composition such that almost all their aluminum and alkali metals (sodium and potassium) are combined as feldspar. This

2550-467: Is followed by deposition of albite , lepidolite , gem tourmaline , beryl, spodumene, amblygonite , topaz , apatite , and fluorite , which may partially replace some of the minerals in the earlier zone. The center of the pegmatite may have cavities lined with spectacular gemstone crystals. Some pegmatites have more complex zoning. Five distinct zones are recognized in the Harding Pegmatite in

2635-489: Is found. Pegmatites are found as irregular dikes , sills , or veins , and are most common at the margins of batholiths (great masses of intrusive igneous rock). Most are closely related spatially and genetically to large intrusions. They may take the form of veins or dikes in the intrusion itself, but more commonly, they extend into the surrounding country rock, especially above the intrusion. Some pegmatites surrounded by metamorphic rock have no obvious connection to

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2720-433: Is limited by the amount of thermal energy available, which must be replenished by crystallization of higher-melting minerals in the magma. Thus, the magma is melting crustal rock at its roof while simultaneously crystallizing at its base. This results in steady contamination with crustal material as the magma rises. This may not be evident in the major and minor element chemistry, since the minerals most likely to crystallize at

2805-463: Is located at the boundary of Rosynsko- Tikychki , Dnistersko - Buzki . This article about a location in Ukraine is a stub . You can help Misplaced Pages by expanding it . This geology article is a stub . You can help Misplaced Pages by expanding it . This geomorphology article is a stub . You can help Misplaced Pages by expanding it . Pegmatite A pegmatite is an igneous rock showing

2890-460: Is on the order of magnitude of one to a few hundred meters. Compared to typical igneous rocks they are rather inhomogeneous and may show zones with different mineral assemblages. Crystal size and mineral assemblages are usually oriented parallel to the wall rock or even concentric for pegmatite lenses. Modern pegmatite classification schemes are strongly influenced by the depth-zone classification of granitic rocks published by Buddington (1959), and

2975-404: Is permeated by sheets and channels of light granitic rock (the leucosome ). The leucosome is interpreted as partial melt of a parent rock that has begun to separate from the remaining solid residue (the melanosome). If enough partial melt is produced, it will separate from the source rock, become more highly evolved through fractional crystallization during its ascent toward the surface, and become

3060-454: Is relieved when overlying material is removed by erosion or other processes. Chemical weathering of granite occurs when dilute carbonic acid , and other acids present in rain and soil waters, alter feldspar in a process called hydrolysis . As demonstrated in the following reaction, this causes potassium feldspar to form kaolinite , with potassium ions, bicarbonate, and silica in solution as byproducts. An end product of granite weathering

3145-411: Is some concern that some granite sold as countertops or building material may be hazardous to health. Dan Steck of St. Johns University has stated that approximately 5% of all granite is of concern, with the caveat that only a tiny percentage of the tens of thousands of granite slab types have been tested. Resources from national geological survey organizations are accessible online to assist in assessing

3230-479: Is that magma will rise through the crust as a single mass through buoyancy . As it rises, it heats the wall rocks , causing them to behave as a power-law fluid and thus flow around the intrusion allowing it to pass without major heat loss. This is entirely feasible in the warm, ductile lower crust where rocks are easily deformed, but runs into problems in the upper crust which is far colder and more brittle. Rocks there do not deform so easily: for magma to rise as

3315-410: Is the case when K 2 O + Na 2 O + CaO > Al 2 O 3 > K 2 O + Na 2 O. Such granites are described as normal or metaluminous . Granites in which there is not enough aluminum to combine with all the alkali oxides as feldspar (Al 2 O 3 < K 2 O + Na 2 O) are described as peralkaline , and they contain unusual sodium amphiboles such as riebeckite . Granites in which there

3400-485: Is typical of a larger family of granitic rocks , or granitoids , that are composed mostly of coarse-grained quartz and feldspars in varying proportions. These rocks are classified by the relative percentages of quartz, alkali feldspar, and plagioclase (the QAPF classification ), with true granite representing granitic rocks rich in quartz and alkali feldspar. Most granitic rocks also contain mica or amphibole minerals, though

3485-409: Is typically orthoclase or microcline and is often perthitic . The plagioclase is typically sodium-rich oligoclase . Phenocrysts are usually alkali feldspar. Granitic rocks are classified according to the QAPF diagram for coarse grained plutonic rocks and are named according to the percentage of quartz , alkali feldspar ( orthoclase , sanidine , or microcline ) and plagioclase feldspar on

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3570-428: Is uncommon, is classified simply as quartz-rich granitoid or, if composed almost entirely of quartz, as quartzolite . True granites are further classified by the percentage of their total feldspar that is alkali feldspar. Granites whose feldspar is 65% to 90% alkali feldspar are syenogranites , while the feldspar in monzogranite is 35% to 65% alkali feldspar. A granite containing both muscovite and biotite micas

3655-512: The Black Hills of South Dakota , and beryl crystals 8.2 meters (27 ft) long and 1.8 meters (6 ft) in diameter have been found at Albany, Maine . The largest beryl crystal ever found was from Malakialina on Madagascar, weighing about 380 tons, with a length of 18 m (59 ft) and a crosscut of 3.5 m (11 ft). Pegmatite bodies are usually of minor size compared to typical intrusive rock bodies. Pegmatite body size

3740-503: The Picuris Mountains of northern New Mexico , US. These are: Large crystals nucleate on the margins of pegmatites, becoming larger as they grow inward. These include very large conical alkali feldspar crystals. Aplites are commonly present. These may cut across the pegmatite, but also form zones or irregular patches around coarser material. The aplites are often layered, showing evidence of deformation. Xenoliths may be found in

3825-459: The texture known as graphic granite . The term was first used by René Just Haüy in 1822 as a synonym for graphic granite . Wilhelm Karl Ritter von Haidinger first used the term in its present meaning in 1845. Pegmatites are exceptionally coarse-grained igneous rocks composed of interlocking crystals , with individual crystals usually over 1 centimeter (0.4 in) in size and sometimes exceeding 1 meter (3 ft). Most pegmatites have

3910-567: The A-Q-P half of the diagram. True granite (according to modern petrologic convention) contains between 20% and 60% quartz by volume, with 35% to 90% of the total feldspar consisting of alkali feldspar . Granitic rocks poorer in quartz are classified as syenites or monzonites , while granitic rocks dominated by plagioclase are classified as granodiorites or tonalites . Granitic rocks with over 90% alkali feldspar are classified as alkali feldspar granites . Granitic rock with more than 60% quartz, which

3995-598: The European Union safety standards (section 4.1.1.1 of the National Health and Engineering study) and radon emission levels well below the average outdoor radon concentrations in the US. Granite and related marble industries are considered one of the oldest industries in the world, existing as far back as Ancient Egypt . Major modern exporters of granite include China, India, Italy, Brazil, Canada, Germany, Sweden, Spain and

4080-490: The Ginsburg & Rodionov (1960) and Ginsburg et al. (1979) classification which categorized pegmatites according to their depth of emplacement and relationship to metamorphism and granitic plutons. Cerny’s (1991) revision of that classification scheme is widely used, Cerny’s (1991) pegmatite classification, which is a combination of emplacement depth, metamorphic grade and minor element content, has provided significant insight into

4165-676: The Kibara Belt of Rwanda and Democratic Republic of the Congo , the Kenticha mine of Ethiopia the Alto Ligonha Province of Mozambique , and the Mibra (Volta) mine of Minas Gerais , Brazil. Notable pegmatite occurrences are found worldwide within the major cratons , and within greenschist -facies metamorphic belts. However, pegmatite localities are only well recorded when economic mineralisation

4250-504: The United States. The Red Pyramid of Egypt ( c.  2590 BC ), named for the light crimson hue of its exposed limestone surfaces, is the third largest of Egyptian pyramids . Pyramid of Menkaure , likely dating 2510 BC, was constructed of limestone and granite blocks. The Great Pyramid of Giza (c. 2580 BC ) contains a huge granite sarcophagus fashioned of "Red Aswan Granite". The mostly ruined Black Pyramid dating from

4335-419: The base of the chamber are the same ones that would crystallize anyway, but crustal assimilation is detectable in isotope ratios. Heat loss to the country rock means that ascent by assimilation is limited to distance similar to the height of the magma chamber. Physical weathering occurs on a large scale in the form of exfoliation joints , which are the result of granite's expanding and fracturing as pressure

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4420-418: The big difference in rheology between mafic and felsic magmas makes this process problematic in nature. Granitization is an old, and largely discounted, hypothesis that granite is formed in place through extreme metasomatism . The idea behind granitization was that fluids would supposedly bring in elements such as potassium, and remove others, such as calcium, to transform a metamorphic rock into granite. This

4505-455: The body of the pegmatite, but their original mineral content is replaced by quartz and alkali feldspar, so that they are difficult to distinguish from the surrounding pegmatite. Pegmatite also commonly replaces part of the surrounding country rock. Because pegmatites likely crystallize from a fluid-dominated phase, rather than a melt phase, they straddle the boundary between hydrothermal mineral deposits and igneous intrusions . Although there

4590-488: The body of the pegmatite. The crystals are never aligned in a way that would indicate flow, but are perpendicular to the walls. This implies formation in a static environment. Some pegmatities take the form of isolated pods, with no obvious feeder conduit. As a result, metamorphic or metasomatic origins have sometimes been suggested for pegmatites. A metamorphic pegmatite would be formed by removal of volatiles from metamorphic rocks, particularly felsic gneiss , to liberate

4675-426: The classification is the petrogenetic component of the classification, which shows the association of LCT pegmatites with mainly orogenic plutons, and NYF pegmatites with mainly anorogenic plutons. Lately, there have been a few attempts to create a new classification for pegmatites less dependent on mineralogy and more reflective of their geological setting. On this issue, one of the most notable efforts on this matter

4760-481: The composition of granite while nepheline syenite pegmatite is a pegmatite with the composition of nepheline syenite. However, the British Geological Survey (BGS) discourages this usage, preferring terms like biotite-quartz-feldspar pegmatite for a pegmatite with a typical granitic composition, dominated by feldspar with lesser quartz and biotite. Under BGS terminology, a pegmatitic rock (for example,

4845-404: The division between S-type (produced by underplating) and I-type (produced by injection and differentiation) granites, discussed below. The composition and origin of any magma that differentiates into granite leave certain petrological evidence as to what the granite's parental rock was. The final texture and composition of a granite are generally distinctive as to its parental rock. For instance,

4930-467: The early 16th century became known as spolia . Through the process of case-hardening , granite becomes harder with age. The technology required to make tempered metal chisels was largely forgotten during the Middle Ages. As a result, Medieval stoneworkers were forced to use saws or emery to shorten ancient columns or hack them into discs. Giorgio Vasari noted in the 16th century that granite in quarries

5015-402: The final melt fraction of a crystallizing body of magma. However, it is difficult to get a representative composition of a pegmatite, due to the large size of the constituent mineral crystals. Hence, pegmatite is often characterised by sampling the individual minerals that compose the pegmatite, and comparisons are made according to mineral chemistry. A common error is to assume that the wall zone

5100-579: The first magma to enter solidifies and provides a form of insulation for later magma. These mechanisms can operate in tandem. For example, diapirs may continue to rise through the brittle upper crust through stoping , where the granite cracks the roof rocks, removing blocks of the overlying crust which then sink to the bottom of the diapir while the magma rises to take their place. This can occur as piecemeal stopping (stoping of small blocks of chamber roof), as cauldron subsidence (collapse of large blocks of chamber roof), or as roof foundering (complete collapse of

5185-684: The grotto is a highly regarded piece of Buddhist art , and along with the temple complex to which it belongs, Seokguram was added to the UNESCO World Heritage List in 1995. Rajaraja Chola I of the Chola Dynasty in South India built the world's first temple entirely of granite in the 11th century AD in Tanjore , India . The Brihadeeswarar Temple dedicated to Lord Shiva was built in 1010. The massive Gopuram (ornate, upper section of shrine)

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5270-556: The hydrous phase is completely depolymerized, existing almost entirely as orthosilicate , with all oxygen bridges between silicon ions broken. The low viscosity promotes rapid diffusion through the fluid, allowing growth of large crystals. When this hydrous fluid is injected into the surrounding country rock , minerals crystallize from the outside in to form a zoned pegmatite, with different minerals predominating in concentric zones. A typical sequence of deposition begins with microcline and quartz, with minor schorl and garnet . This

5355-418: The last fluid fraction of a large crystallizing magma body. This residual fluid is highly enriched in volatiles and trace elements, and its very low viscosity allows components to migrate rapidly to join an existing crystal rather than coming together to form new crystals. This allows a few very large crystals to form. While most pegmatites have a simple composition of minerals common in ordinary igneous rock,

5440-474: The lower crust , rather than by decompression of mantle rock, as is the case with basaltic magmas. It has also been suggested that some granites found at convergent boundaries between tectonic plates , where oceanic crust subducts below continental crust, were formed from sediments subducted with the oceanic plate. The melted sediments would have produced magma intermediate in its silica content, which became further enriched in silica as it rose through

5525-697: The lower continental crust at high thermal gradients. This leads to significant extraction of hydrous felsic melts from granulite-facies resitites. A-type granites occur in the Koettlitz Glacier Alkaline Province in the Royal Society Range, Antarctica. The rhyolites of the Yellowstone Caldera are examples of volcanic equivalents of A-type granite. M-type granite was later proposed to cover those granites that were clearly sourced from crystallized mafic magmas, generally sourced from

5610-456: The magma is crystallized. Otherwise, the separation of the fluid phase is difficult to explain. Granite requires a water content of 4 wt% at a pressure of 0.5  GPa (72,500  psi ), but only 1.5 wt% at 0.1 GPa (14,500 psi) for phase separation to take place. The volatiles (primarily water, borates , fluorides , chlorides , and phosphates ) are concentrated in the hydrous phase, greatly lowering its viscosity. The silica in

5695-435: The magma is inevitable once enough magma has accumulated. However, the question of precisely how such large quantities of magma are able to shove aside country rock to make room for themselves (the room problem ) is still a matter of research. Two main mechanisms are thought to be important: Of these two mechanisms, Stokes diapirism has been favoured for many years in the absence of a reasonable alternative. The basic idea

5780-426: The magma. Other processes must produce these great volumes of felsic magma. One such process is injection of basaltic magma into the lower crust, followed by differentiation, which leaves any cumulates in the mantle. Another is heating of the lower crust by underplating basaltic magma, which produces felsic magma directly from crustal rock. The two processes produce different kinds of granites, which may be reflected in

5865-408: The magmatic parent of granitic rock. The residue of the source rock becomes a granulite . The partial melting of solid rocks requires high temperatures and the addition of water or other volatiles which lower the solidus temperature (temperature at which partial melting commences) of these rocks. It was long debated whether crustal thickening in orogens (mountain belts along convergent boundaries )

5950-405: The mantle. Although the fractional crystallisation of basaltic melts can yield small amounts of granites, which are sometimes found in island arcs, such granites must occur together with large amounts of basaltic rocks. H-type granites were suggested for hybrid granites, which were hypothesized to form by mixing between mafic and felsic from different sources, such as M-type and S-type. However,

6035-653: The origin of pegmatitic melts and their relative degrees of fractionation. Granitic pegmatites are commonly ranked into three hierarchies (class – family – type – subtype) depending upon their mineralogical-geochemical characteristics and depth of emplacement according to Cerny (1991). Classes are Abyssal, Muscovite, Rare-Element and Miarolitic. The Rare-Element Class is subdivided based on composition into LCT and NYF families: LCT for Lithium, Cesium, and Tantalum enrichment and NYF for Niobium, Yttrium, and Fluorine enrichment. Most authors classify pegmatites according to LCT- and NYF-types and subtypes. Another important contribution of

6120-441: The overlying crust. Early fractional crystallisation serves to reduce a melt in magnesium and chromium, and enrich the melt in iron, sodium, potassium, aluminum, and silicon. Further fractionation reduces the content of iron, calcium, and titanium. This is reflected in the high content of alkali feldspar and quartz in granite. The presence of granitic rock in island arcs shows that fractional crystallization alone can convert

6205-465: The primary source of lithium either as spodumene, lithiophyllite or usually from lepidolite. The primary source for caesium is pollucite , a mineral from a zoned pegmatite. The majority of the world's beryllium is sourced from non-gem quality beryl within pegmatite. Tantalum, niobium, and rare-earth elements are sourced from a few pegmatites worldwide, such as the Greenbushes Pegmatite ,

6290-702: The reign of Amenemhat III once had a polished granite pyramidion or capstone, which is now on display in the main hall of the Egyptian Museum in Cairo (see Dahshur ). Other uses in Ancient Egypt include columns , door lintels , sills , jambs , and wall and floor veneer. How the Egyptians worked the solid granite is still a matter of debate. Tool marks described by the Egyptologist Anna Serotta indicate

6375-439: The right constituents and water, at the right temperature. A metasomatic pegmatite would be formed by hydrothermal circulation of hot alteration fluids upon a rock mass, with bulk chemical and textural change. Metasomatism is currently not favored as a mechanism for pegmatite formation and it is likely that metamorphism and magmatism are both contributors toward the conditions necessary for pegmatite genesis. Most pegmatites have

6460-551: The risk factors in granite country and design rules relating, in particular, to preventing accumulation of radon gas in enclosed basements and dwellings. A study of granite countertops was done (initiated and paid for by the Marble Institute of America) in November 2008 by National Health and Engineering Inc. of USA. In this test, all of the 39 full-size granite slabs that were measured for the study showed radiation levels well below

6545-418: The rock's high quartz content and dearth of available bases, with the base-poor status predisposing the soil to acidification and podzolization in cool humid climates as the weather-resistant quartz yields much sand. Feldspars also weather slowly in cool climes, allowing sand to dominate the fine-earth fraction. In warm humid regions, the weathering of feldspar as described above is accelerated so as to allow

6630-414: The rocks often bear a close resemblance. Under these conditions, granitic melts can be produced in place through the partial melting of metamorphic rocks by extracting melt-mobile elements such as potassium and silicon into the melts but leaving others such as calcium and iron in granulite residues. This may be the origin of migmatites . A migmatite consists of dark, refractory rock (the melanosome ) that

6715-489: The roof of a shallow magma chamber accompanied by a caldera eruption.) There is evidence for cauldron subsidence at the Mt. Ascutney intrusion in eastern Vermont. Evidence for piecemeal stoping is found in intrusions that are rimmed with igneous breccia containing fragments of country rock. Assimilation is another mechanism of ascent, where the granite melts its way up into the crust and removes overlying material in this way. This

6800-435: The surface than magmas of I-type granites, which are thus more common as volcanic rock (rhyolite). They are also orogenic but range from metaluminous to strongly peraluminous. Although both I- and S-type granites are orogenic, I-type granites are more common close to the convergent boundary than S-type. This is attributed to thicker crust further from the boundary, which results in more crustal melting. A-type granites show

6885-440: The texture is known as porphyritic . A granitic rock with a porphyritic texture is known as a granite porphyry . Granitoid is a general, descriptive field term for lighter-colored, coarse-grained igneous rocks. Petrographic examination is required for identification of specific types of granitoids. Granites can be predominantly white, pink, or gray in color, depending on their mineralogy . The alkali feldspar in granites

6970-502: The uranium washes into the sediments from the granite uplands and associated, often highly radioactive pegmatites. Cellars and basements built into soils over granite can become a trap for radon gas, which is formed by the decay of uranium. Radon gas poses significant health concerns and is the number two cause of lung cancer in the US behind smoking. Thorium occurs in all granites. Conway granite has been noted for its relatively high thorium concentration of 56±6 ppm. There

7055-599: The use of flint tools on finer work with harder stones, e.g. when producing the hieroglyphic inscriptions. Patrick Hunt has postulated that the Egyptians used emery , which has greater hardness. The Seokguram Grotto in Korea is a Buddhist shrine and part of the Bulguksa temple complex. Completed in 774 AD, it is an artificial grotto constructed entirely of granite. The main Buddha of

7140-405: Was sufficient to produce granite melts by radiogenic heating , but recent work suggests that this is not a viable mechanism. In-situ granitization requires heating by the asthenospheric mantle or by underplating with mantle-derived magmas. Granite magmas have a density of 2.4 Mg/m , much less than the 2.8 Mg/m of high-grade metamorphic rock. This gives them tremendous buoyancy, so that ascent of

7225-564: Was supposed to occur across a migrating front. However, experimental work had established by the 1960s that granites were of igneous origin. The mineralogical and chemical features of granite can be explained only by crystal-liquid phase relations, showing that there must have been at least enough melting to mobilize the magma. However, at sufficiently deep crustal levels, the distinction between metamorphism and crustal melting itself becomes vague. Conditions for crystallization of liquid magma are close enough to those of high-grade metamorphism that

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