crystals that are several meters in length and weigh over one ton. Pegmatite is an exceptionally coarse-grained plutonic igneous rock.Most pegmatites have a mineralogical composition of granite but composition has no defining importance here. Although no mineable tin deposits are known in Wyoming, slightly elevated tin concentrations are found in pegmatites and associated with metals deposits in the southern Laramie Mountains, the southern Medicine Bow Mountains, the South Pass area, and the Sierra Madre. major cratons, and within greenschist-facies metamorphic belts. branches or offshoots of igneous bodies) within the aureole of some granites. It will form from waters that separate from a magma in the late stages of crystallization. are completely obliterated by late-stage hydrothermal reworking (metasomatism). There is little doubt that some of these those containing tourmaline. Some pegmatites have a gas cavity at the center of the pegmatite. aegirine, exotic carbonate minerals, natrolite and various other zeolites. formally or informally as a class of intrusive rock or within a larger igneous In most cases, there is no particular genetic significance to the presence of rare mineralogy within a pegmatite, however it is possible to see some causative and genetic links between, say, tourmaline-bearing granite dikes and tourmaline-bearing pegmatites within the area of influence of a composite granite intrusion (Mount Isa Inlier, Queensland, Australia). It is most often sold commercially as a granite product. They also can be a source of gemstones. This is because of the difficulty in Overall pegmatite rock has very few uses. Individual crystals over 10 metres (33 ft) These include spodumene, microcline, beryl, and tourmaline.[3]. Mineral replacement producing pseudomorphs of pock- et minerals, such as clay minerals after spodumene (kunz- ite) in some of the pegmatite bodies in the Pala district, appears to have occurred either prior to or in the absence of pocket rupture. Geological setting of the kakortokite series and associated pegmatites and mineral veins The Ilímaussaq alkaline complex (Fig. There is often no meaningful way to distinguish pegmatites Pegmatite is also used as a primary ingredient for making glass and ceramics, and as a filler for many other products. Large sheets of mica are mined from is used as a primary ingredient for making glass and ceramics. hydrothermal processes involving aqueous (and, in some cases, F- or CO3-rich) Gem tourmaline, in mostly blue and green colours is associated with coarse muscovite and/or quartz crystals in pods and veins often elongate parallel to the strike of pegmatite. Tantalum, niobium, rare-earth elements are sourced from a few pegmatites worldwide, notably the Greenbushes Pegmatite. Basically, the presence of residual water has allowed the magma to cool slowly to permit coarse crystal growth. Worldwide, notable pegmatite occurrences are within the Canadian Mineralogist Special Publication 10, 347 pp. Because of their varied, it is estimating the modal abundance of mineral 4 issue, shown dirty and as a newly mined piece from finds in the fall of 2012. However, pegmatite localities are only well recorded when economic mineralisation is found. The piece was illustrated in the original article on these optimistic efforts on page 312, figure 7 in the 2013 Rocks and Minerals vol. Pegmatite lithium deposits, also known as hard rock lithium deposits, can contain extractable amounts of a number of elements, including lithium, tin, tantalum and niobium. The mineral pollucite is the main source of the metal cesium. Individual crystals over 10 metres (33 ft) long have been found, and many of the world's largest crystals were found within pegmatites. Although pegmatites having gross compositions similar to other rock types are known, their composition is generally that of granite; the composition may be simple or complex and may include rare minerals rich in such elements as lithium, boron, fluorine, niobium, tantalum, uranium, and rare earths. minerals crystallized from super-evolved melts left over after the formation of of a batholith. Complex pegmatites result because of the presence exotic volatiles such as chlorine, fluorine, and carbon dioxide. Mica is used to make optical elements in electronics. (2021). There is often no meaningful way to distinguish pegmatites according to chemistry due to the difficulty of obtaining a representative sample, but often groups of pegmatites can be distinguished on contact textures, orientation, accessory minerals and timing. long have been found, and many of the world’s largest crystals were found Pegmatite is used in Pegmatites contain exceptionally large crystals and they contain rarely minerals than other types of rocks. loparite), Li (mangan-neptunite, tainiolite), Be (leucophanite, epididymite, fluids, which leave their distinct mineralogical overprint, like the The extreme conditions of crystallization sometimes produce It is also used Similarly, pegmatite is often found within the contact zone of granite, transitional with some greisens, as a late-stage magmatic-hydrothermal effect of syn-metamorphic granitic magmatism. on the interpretations of the investigating geologist. Compositions of feldspars, muscovite, and garnet show some regional variation, but are generally similar for pegmatites and associated granodiorite. Pegmatite can also form in fractures that develop on the If the pegmatite is sound and attractive, it might be cut Pegmatites is intruding mafic and carbonate-bearing While difficult to be certain of derivation of pegmatite in the strictest sense, often pegmatites are referred to as "metamorphic", "granitic" or "metasomatic", based on the interpretations of the investigating geologist. Li-bearing or Li-mineral bearing pegmatite, or “boron pegmatite” for Sometimes pegmatite is mined for its minerals, including mica and feldspar. pegmatite include most minerals associated with granite and granite-associated Pegmatites may have any imaginative magmatic composition and they are actually known to contain a large number of unusual minerals. Beryl saturation in granitic melts depends on a number of factors. Most pegmatites are composed of quartz, feldspar and mica, having a similar silicic composition as granite. the strictest sense, often pegmatites are referred to as They are most Granite pegmatites can be complex in composition and contain a diverse suite of exotic minerals and tend to be enriched in what geologists call “incompatible elements" or "rare elements." Occasionally, enrichment in the unusual trace elements will result in crystallisation of equally unusual and rare minerals such as beryl, tourmaline, columbite, tantalite, zinnwaldite and so forth. Apart from microcline and amazonite, the principal minerals of pegmatites include albite and quartz, the secondary minerals include biotite, fluorite, magnetite, garnet, and the accessory minerals include gadolinite, tantalite-columbite, genthelvite, fergusonite, cyrtolite, and galena, and more rarely yttrialite, thorite, pyrochlore, samarskite, and beryl. Usually seeing that London, D. (2008): Pegmatites. “metamorphic”, “granitic” or “metasomatic”, based accompanied by pegmatites, veins, lenses and pods of coarse-crystalline (nepheline, sodalite, alkali feldspars, aegirine and sodic amphiboles), as well They have been mined for over 100 years for potash feldspar, with occasional supplementary pro­ It has limited use as an architectural stone and is sometimes encountered in a dimension stone quarry that is producing granite. Rarer "intermediate" and "mafic" pegmatite containing amphibole, Ca-plagioclase feldspar, pyroxene and other minerals are known, found in recrystallised zones and apophyses associated with large layered intrusions. Pegmatites are important because they often contain rare earth minerals and gemstones,[5] such as aquamarine, tourmaline, topaz, fluorite, apatite and corundum, often along with tin and tungsten minerals, among others. The dikes and pockets are small in size, taking place underground following a dike or a small pocket. porphyry dikes and veins may intrude pegmatites and wall rocks adjacent to 1. Pegmatites associated with granitic domes within the Archaean Yilgarn Craton intruding ultramafic and mafic rocks contain red, orange and brown almandine garnet. other products. So its concentration in the melt grows as crystallization progresses. Syenite pegmatites are quartz depleted and contain large Rarer intermediate composition and mafic pegmatites containing amphibole, Ca-plagioclase feldspar, pyroxene, feldspathoids and other unusual minerals are known, found in recrystallised zones and apophyses associated with large layered intrusions. tungsten, and many other elements. [online] Available at: https://geologyscience.com/rocks/pegmatite/ [16th January 2021 ], Economically Important Metal Concentrations in Earth’s Crust, Porphyry Deposits: General characteristics and modeling, https://en.wikipedia.org/w/index.php?title=Pegmatite&oldid=872883451, https://geologyscience.com/rocks/pegmatite/. However, gem deposits refer only to those of granitic composition. Most pegmatites are composed of quartz, feldspar and mica; in essence a " granite ". mineral of interest, for instance “lithian pegmatite” to describe a pegmatitic. Pegmatite bodies are usually of minor size compared to typical intrusive rock bodies. These cavities range from several inches to more than a foot in length and often contain large crystals with fully developed crystal faces. retardation plates, circuit boards, optical filters, detector windows, and many Pegmatites can be classified according to the elements or feldspar, frequently with mica and generally with quartz. Many are excellent-quality and are large crystals. pegmatite include: amazonite, apatite, aquamarine, beryl, chrysoberyl, emerald, Igneous rocks formed large crystals are usually ttributed to a slow rate of crystallization but with pegmatites’ large crystals are attributed to low-viscosity fluids that allow ions to be very mobile.During the crystallization stage, the melt usually contains a significant amount of dissolved water and other volatiles such as chlorine, fluorine, and carbon dioxide. Rocks with similar texture to pegmatites are called 3). Feldspar within a pegmatite may display exaggerated and perfect twinning, exsolution lamellae, and when affected by hydrous crystallization, macroscale graphic texture is known, with feldspar and quartz intergrown. Crystal size and mineral assemblages are usually oriented parallel to the wall rock or even concentric for pegmatite lenses.[4]. The major lithium ore minerals are The most common of these are mica, quartz and feldspar, the minerals associated with granite. This page was last edited on 12 January 2021, at 23:31. Aplite and rare mineral mining. Rare mineral specimen from Kola peninsula, Russia. Most pegmatites are found in sheets of rock (dikes and veins) near large masses of igneous rocks called batholiths. Hence, pegmatite is often characterised by sampling the individual minerals that compose the pegmatite, and comparisons are made according to mineral chemistry. Thus, the possible growth mechanisms in a wide variety of known pegmatites may likely involve a combination of the following processes; Despite this hypothesis on likely chemical, thermal and compositional conditions required to promote pegmatite growth there are three main theories behind pegmatite formation; Metasomatism is currently not well 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. Pegmatites usually do not support large mining operations. sample, but often groups of pegmatites can be distinguished on contact 88, no. 15 T.26N. material comprising the same minerals as found in the surrounding rocks Worldwide, notable pegmatite occurrences are within the major cratons, and within greenschist-facies metamorphic belts. as copious quantities of rare minerals enriched in water and incompatible trace The single feature that is diagnostic to all pegmatites is their large size crystal components. These include cesium, rubidium, lithium, beryllium, tantalum, niobium, tin, boron, and zirconium, along with a few others. Pegmatite is the host rock for numerous mineral deposits and can be the commercial sources of beryllium, bismuth, tin, titanium, tungsten, niobium, and many other elements. Sadly, this pegmatite is now completely mined out and stripped. The pegmatite mineralogy is dominated by some form offeldspar, frequently with mica and generally with quartz. textures, orientation, accessory minerals and timing. 2. intrusions, creating a confused sequence of felsic intrusive apophyses (thin centimeters to meters across. The major mineral constituents of the pegmatites are relatively similar throughout the district. or, to distinsguish them from their granitic counterparts, alkaline pegmatites. decorative stone products and sold commercially as a “granite.”. However, It is impossible to quantify the mineralogy.Because of their varied, it is estimating the modal abundance of mineralspecies which are of only a trace amount. Most pegmatites are found in sheets of rock (dikes and veins) near large masses of igneous rocks called batholiths. chkalovite) and Th (steenstrupine). The product of pegmatite decomposition is euclase. These are used to make components for electronic devices, A few of the pegmatites are more fractionated and contain tourmaline and beryl. species which are of only a trace amount. Pegmatites association. Common accessory minerals include garnet, tourmaline, and apatite. While pegmatite occurrences are not uncommon, those bearing gem-quality minerals in mineable quantities are exceedingly r… Media related to Pegmatite at Wikimedia Commons. Crystal size is the most striking feature of pegmatites, with crystals usually over 5 cm in size. crystallization; this activity often occurs in small pockets along the margins gemstone mining because of it has large crystal minerals. “to bind together”, Texture: Phaneritic sequences include garnet, commonly almandine or spessartine. The minerals found in pegmatite veins may be divided into three general divisions. REE (rinkolite, belovite), Zr (eudialyte, lovozerite, catapleiite), Nb (labuntsovite, form from waters that separate from a magma in the late stages of Pegmatites are sometimes sources of valuable minerals such as spodumene (an ore of lithium) and beryl (an ore of beryllium) that are rarely found in economic amounts in other types of rocks. Compared to typical igneous rocks they are rather inhomogeneous and may show zones with different mineral assemblages. as a filler in many products. Syenite pegmatites are quartz depleted and contain large feldspathoid crystals instead. counting and sampling mineral grains in a rock which may have crystals from Other elements that may be sourced from pegmatite include tantalum, niobium, bismuth, molybdenum, tin, tungsten, and the rare earths. frequently mined for industrial minerals. This is because of the difficulty in counting and sampling mineral grains in a rock which may have crystals from centimeters to meters across. Within the metamorphic belts, pegmatite tends to concentrate around granitic bodies within zones of low mean strain and within zones of extension, for example within the strain shadow of a large rigid granite body. Geochemically, pegmatites typically have major element compositions approximating "granite", however, when found in association with granitic plutons it is likely that a pegmatite dike will have a different trace element composition with greater enrichment in large-ion lithophile (incompatible) elements, boron, beryllium, aluminium, potassium and lithium, uranium, thorium, cesium, et cetera. bismuth, boron, cesium, lithium, molybdenum, niobium, tantalum, titanium, Of interest are a group of minerals that contain the rare earth metals, or those elements with atomic number 57–71 (lanthanum to … Often, bulk samples of some 50–60 kg of rock must be crushed to obtain a meaningful and repeatable result. Microscopically, the studied pegmatites hosted within the monzogranite are composed essentially of potash feldspar, quartz, plagioclase, and mafic minerals (biotite, hornblende) with grains reached up to 2 cm (Fig. Secondary minerals, formed by subsolidus recrystallization, include epidote, muscovite, quartz, and grossular garnet. Beyond that, pegmatite may include most minerals associated with granite and granite-associated hydrothermal systems, granite-associated mineralisation styles, for example greisens, and somewhat with skarn associated mineralisation. term of pegmatite derives from Homeric Greek, πήγνυμι (pegnymi), which means The extreme conditions may produce crystals many feet in length and may weigh more than a ton. Pegmatite is difficult to sample representatively due to the large size of the constituent mineral crystals. Early crystallization process, water is not removed. Pegmatites can be classified according to the elements or mineral of interest, for instance "lithian pegmatite"[7] to describe a Li-bearing or Li-mineral bearing pegmatite, or "boron pegmatite" for those containing tourmaline. Rare elements concentrated in large crystals may make pegmatite a potential source of valuable ore. Pegmatite deposits may also contain gemstones, industrial minerals, and rare minerals. The product of pegmatite decomposition is euclase. It is here associated with blue-green K feldspar, beryl, bertrandite, phenakite and other rare minerals (WGNHS files, 1986). Large sheets of mica are often mined from pegmatite and used to make components electronic devices, circuit boards, optical filters, detector windows, and many other products. The ions in the water are much more mobile than ions in the melt. Example of a very large crystal minerals with mica and generally with quartz others are over. 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