Moore, P.B. Les pegmatites sont des roches ignées intrusives formées de cristaux plus grands que 1 cm. PEGMATITE is a common plutonic rock, of variable texture and coarseness, that is composed of interlocking crystals of widely different sizes. The lower whitish part of the rock does not show a pegmatitic texture. 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. Consequently, the pegmatoids are strongly magnetic compared to ophitic units. Examples from the Weiss Mine, Germany, show this transition. American Mineralogist, 43, 181-207. Pegmatite à clinopyroxène et plagioclase : des lentilles de pyroxène forment un cumulat. It has been termed pegmatite in some occurrences, and granite in others. 2. The pegmatite mineralogy is dominated by some form offeldspar, frequently with mica and generally with quartz. Varlamoff, N. (1958-1959) Zonéographie de quelques champs pegmatitiques de l'Afrique centrale et les classifications de K.A. Lithothèque ENS de Lyon. Pegmatites may have any imaginative magmatic composition and they are actually known to contain a large number of unusual minerals. (1958) Pegmatite phosphates and their problems. The word "pegmatite" comes from the Greek word pegnymi, which means "to bind together," referring to the entwined feldspar and quartz crystals commonly found in the rock. Instead, the large crystals of a pegmatite formed in a magma that was extra rich in dissolved water. It usually contains small quantities of mica or hornblende, and minor accessory minerals may be present. Pegmatite (Pegmatite à texture graphique) Massif armoricain Roscoff . La pegmatite est une roche magmatique à grands cristaux de taille supérieure à 20 mm, et pouvant atteindre plusieurs mètres. Today it is ap- plied to any crystalline roclz that is, at least in part, ex- tremely coarse grained. Most pegmatites are found in sheets of rock (dikes and veins) near large masses of igneous rocks called batholiths. A pegmatite is an igneous rock, formed underground, with interlocking crystals usually larger than 2.5 cm in size (1 in). La dernière modification de cette page a été faite le 24 octobre 2020 à 19:42. To be called a pegmatite, a rock should be composed almost entirely of crystals that are at least one centimeter in diameter. Granite is an intrusive igneous rock which is very hard, crystalline and is visibly homogeneous in texture and forms by melting of continental rocks Pegmatite rock is holocrystalline, intrusive igneous rock which is formed by partial melting and dewatering during the … Pegmatites often form in veins that opened up at the end of the crystallization of a large intrusive mass. Pegmatite is an exceptionally coarse-grained plutonic igneous rock.Most pegmatites have a mineralogical composition of granite but composition has no defining importance here. Les pegmatites sont liées génétiquement à un magma de composition granitique car elles correspondent au dernier liquide résiduel (donc très différencié) issu de l'évolution de ce magma. Pegmatite veins are differentiated, and their larger part is occupied by zones of graphic and pegmatoid texture, which sometimes contain large cavities with crystals of feldspars, quartz, topaz, and several other minerals. These are sometimes called granite pegmatites to indicate their mineralogical composition. En gros cristaux automorphes (25 x 15 cm) sans texture graphique, avec microperthites. The term pegmatjte, then, primarily refers to the texture of a roclz, that is, the size, shape, and arrangement of mineral grains. Pegmatite à apatite • Microcline. Nevertheless, rare element pegmatites can have complex internal structures. à abbreviatus aber-ildut aciculaire acides acrocidaris actinocyathus actinostreon actinostreon solitarium actinote actuel aculeatum acuta acuticuspidata adakite adamello adamellogranite adulaire adulaire et épidote aegiromena aegyrine africanus afrique afrique du sud … The complex internal textures of Nb–Ta–Sn oxide minerals from the zones IV–V indicate a distinctly fluid-rich environment at the late stage of crystallization of the Nanping No. A pegmatitic texture is one in which the mineral grains are exceptionally large. L'abondance de l'eau facilite la diffusion des éléments chimiques et permet la croissance des grands cristaux. Pegmatite definition, a coarsely crystalline granite or other high-silica rock occurring in veins or dikes. Résultant de l'intrusion des derniers magmas les plus différenciés dans les plutons granitiques, elles sont en effet plus riches en fluides hydrothermaux (produits par démixtion du magma résiduel) et éléments incompatibles (concentration dans les liquides silicatés résiduels, d’éléments normalement rares tels que Li, No, Cs, Zi, F, B, Be, Sn, Ta, Nb, U, lanthanides dont les terres rares, qui peuvent donner lieu à exploitation) que les magmas granitiques, et se caractérisent par la présence de minéraux particuliers dits pneumatolytiques (en) (lépidolite, phlogopite, topaze, béryl, tourmaline, etc.)[1]. The water allowed the necessary elements to diffuse extra fast to the sites of crystallization. This is because of the difficulty incounting and sampling mineral grains in a rock which may have crystals from… The extra large size does not mean that they cooled extra slowly. 31 pegmatite. Fisher, D.J. The extra large size does not mean that they cooled extra slowly. Vlassov et de A.I. Miarolitic cavities (or miarolitic texture) are typically crystal-lined irregular cavities or vugs most commonly found in granitic pegmatites, and also in a variety of igneous rocks.The central portions of pegmatites are often miarolitic as the pegmatite dike crystallizes from the outside walls toward the center. Caractéristique des pegmatites sont des minéraux riches en composants volatils: Miche, la plupart du temps blanc, le type muscovitico ou riche lithium, comme lépidolite, autres minéraux au lithium dont la spodumène, la tourmaline, la fluorine, l ' apatite, la cassitérite, la wolframite et de nombreux minéraux uranifères et les terres rares. (1982) Pegmatite minerals of P(V) and B(III). Most pegmatites have a composition that is similar to granite with abundant quartz, feldspar, and mica. Most pegmatites are found in sheets of rock (dikes and veins) near large masses of igneous rocks called batholiths. La pegmatite est une roche ignée ayant une granulométrie très grossière dépassant 20 mm, même parfois avec des cristaux géants, de plusieurs mètres ou milliers de tonnes. Ces roches proviennent de la cristallisation des fluides tardifs d'un magma. Un article de Wikipédia, l'encyclopédie libre. Rocks that display large, granular crystal structure are called "pegmatitic." Faites votre choix parmi Pegmatite de photos, images, illustrations, vecteurs, symboles et vidéos libres de droits sur Adobe Stock et téléchargez-les pour vos projets créatifs. However, compositions such as gabbro pegmatite, syenite pegmatite, and any other plutonic rock name combine… Chargement des images. The largest ones are, by convention, more than about 3 cm long. Sign up for free and download 15 free images every day! Les roches avec cette granulométrie ont une texture pegmatitique. Du fait de la présence des éléments fondants qui abaissent le point de fusion, la viscosité du magma, et le taux de nucléation, le filon lié à l'intrusion magmatique représente une phase pegmatitique (entre 800° et 600°) qui voit l'augmentation du taux de croissance des cristaux et un temps de refroidissement qui n'a pas besoin d'être très long[4]. Cette section est vide, insuffisamment détaillée ou incomplète. As huge amount of time has been granted to pegmatite rocks so it has extremely large crystals and sometimes rare minerals are associated with it … Normally, pegmatites are unzoned and largely uniform in both composition and texture. Pegmatite is an intrusive igneous rock made up of large interlocking crystals. Vous pouvez partager vos connaissances en l’améliorant (comment ?) Guinsbourg. Une pegmatite est une roche qui résulte de la cristallisation d'un magma (liquide silicaté) riche en eau dissoute (et non pas en eau libre). La plupart des roches à texture pegmatitique ont une composition voisine du granite, avec comme minéraux essentiels le quartz, des feldspaths et des micas (muscovite surtout) mais sont appauvries en minéraux mafiques et enrichies en éléments incompatibles. Jean Aubouin, Robert Brousse, Jean Pierre Lehman, https://fr.wikipedia.org/w/index.php?title=Pegmatite&oldid=175886010, Article contenant un appel à traduction en anglais, Article avec une section vide ou incomplète, Catégorie Commons avec lien local identique sur Wikidata, Portail:Sciences de la Terre et de l'Univers/Articles liés, licence Creative Commons attribution, partage dans les mêmes conditions, comment citer les auteurs et mentionner la licence. The product is characterized by normal phaneritic textures that generally are coarse grained. Pegmatite are intrusive rocks with extreme coarse grained texture that are developed at the final stages of magma crystallization. Les pegmatites forment des filons (poches ou veines), en bordure ou au voisinage immédiat des plutons granitiques auxquels elles sont génétiquement associées. These are concentric zones which conform roughly to the shape of the pegmatite body and differ in mineral assemblages and textures. Cliquez sur une vignette pour l’agrandir. En pétrographie, la texture d'une roche (parfois mal appelée « structure », puisque ces deux notions soient différentes), caractérise l'arrangement des cristaux entre eux à l'échelle de l'échantillon, de la lame mince ou même à une échelle plus fine.. On distingue trois groupes de textures fondamentales [4] : . Pegmatite with blue corundum crystals Pegmatite containing lepidolite, tourmaline, and quartz from the White Elephant Mine in the Black Hills, South Dakota. Thousands of new, high-quality pictures added every day. Abstract. The saprock maintains the fabric and textures of the unaltered pegmatite or aplite, whereas the more advanced level of chemical alteration where these features are completely wiped out is called saprolite. Usually seeing thatpegmatite include most minerals associated with granite and granite-associatedhydrothermal systems. See more. Rock-forming minerals of these pegmatites are represented by microcline, amazonite, albite, and quartz; the secondary minerals are micas; and the accessory minerals are garnet, topaz, … The most spectacular pegmatites contain abnormally large crystals mixed with medium sized and smaller crystals. La pegmatite granititique dite Nanping No. Some pegmatite bodies are small irregular patches less than 1 cm. A pegmatite is an igneous rock, formed underground, with interlocking crystals usually larger than 2.5 cm in size (1 in). Instead, the large crystals of a pegmatite formed in a magma that was extra rich in dissolved water. The water allowed the necessary elements to diffuse extra fast to the sites of crystallization. Pegmatite, almost any wholly crystalline igneous rock that is at least in part very coarse grained, the major constituents of which include minerals typically found in ordinary igneous rocks and in which extreme textural variations, especially in grain size, are characteristic. Des filons ou des poches s'injectent dans ces fissures à la périphérie du pluton, formant des pegmatites. Ces fluides se concentrent dans les fissures de retrait qui se forment durant le refroissement d'une masse de magma, ce qui donne une allure filonienne aux roches pegmatitique. The name pegmatite has nothing to do with the mineral composition of the rock. The latter mineral usually forms large crystals that enclose numerous, identically oriented intergrowths of quartz. La composition est très comparable à celle des feldspaths potassiques de la pegmatite à béryl. Find Amazing Natural Patterns Textures Slice Pegmatite stock images in HD and millions of other royalty-free stock photos, illustrations and vectors in the Shutterstock collection. Most of the large igneous minerals that are seen in geology labs are from pegmatites. Granite Pegmatite is a common Igneous rock What is the texture of pegmatite? (also graphic texture and granophyric texture), a term that describes the physical appearance and character of magmatic rocks that exhibit close intergrowths as a result of the simultaneous crystallization of quartz and feldspar. Annales de la Société géologique de Belgique, 82, B55-B87. La pegmatite (du grec pegma, « qui est assemblé, coagulé ») est une roche magmatique à grands cristaux (de taille supérieure à 1 cm, et pouvant atteindre plusieurs mètres), fréquemment automorphes. pegmatite in the early 1800s to refer to a roclz with a patterned geometric intergrowth of feldspar and quartz (now commonly termed graphic granite). Texturally, pegmatoids are coarse grained when compared to ophitic zones. Les pegmatites graphiques (du grec graphein, « écrire », l'aspect de cette roche évoquant l'écriture cunéiforme) sont une variété de pegmatites dans lesquelles la cristallisation simultanée du quartz et de feldspath alcalin se manifeste par une disposition régulière de plages de quartz, isolées et cunéiformes, mais formant un unique cristal de quartz au sein du réseau cristallin d'un feldspath : l'intercroissance contemporaine de ces deux cristaux donne une structure pœcilitique[2]. Pegmatite rock is holocrystalline, intrusive igneous rock which is formed by partial melting and dewatering during the process of metamorphism. Other articles where Pegmatitic texture is discussed: rock: Classification by grain or crystal size: 2 inches) are termed pegmatitic. Pegmatites … Crystals up to many meters long have been reported. On note, toutefois, des teneurs plus élevées en Ba et Sr et, inversement, une teneur plus faible en Rb. A pegmatite texture in a rock is a course-grained Igneous Rock. 5.2 Composition 5.2.1 Mineral Content Apatite, Beryl, Feldspar, Fluorite, Garnet, Lepidolite, Quartz, Silica, Spodumene, Topaz This texture is found in intrusive rocks. Coarse plagioclase laths dominate with interstitial, subhedral clinopyroxene and abundant interstitial to somewhat poikilitic magnetite and ilmenite. pegmatite: see granite granite, coarse-grained igneous rock of even texture and light color, composed chiefly of quartz and feldspars. Elles correspondent généralement au liquide résiduel, riche en eau, de fin de cristallisation d'un magma granitique. selon les recommandations du projet minéraux et roches. Most igneous minerals exclude water from their structure, so the last magma to cool often ends up enriched in water and other incompatible elements. 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