Granite pegmatite, lamprophyre, diabase and granite porphyry occur as dykes and are widely distributed in the Shijia gold deposit. Perthite feldspar within a pegmatite often shows gigantic perthitic texture visible to the naked eye. igneous rock: Pegmatites and late-stage mineralization. Omissions? Alkalis are more reactive and volatile. A pegmatite is an igneous rock, formed underground, with interlocking crystals usually larger than 2.5 cm in size (1 in). Template:Refimprove A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5cm in size;1 such rocks are referred to as pegmatitic. Examples of intrusive igneous rocks are diabase, diorite, gabbro, granite, pegmatite, and peridotite. However, compositions such as gabbro pegmatite, syenite pegmatite, and any other plutonic rock name combine… The majority of the world's beryllium is sourced from non-gem quality beryl within pegmatite. A pegmatite is an igneous rock, formed underground, with interlocking crystals usually larger than 2.5 cm in size (1 in). 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. These may be named formally or informally as a class of intrusive rock or within a larger igneous association. A limited amount of chemical data for gabbros from the BUC was reported by Kerr et al. Most pegmatites are composed of quartz, feldspar and mica; in essence a granite. Is the mantle mafic or felsic? 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. [1], The word pegmatite derives from Homeric Greek, πήγνυμι (pegnymi), which means “to bind together”, in reference to the intertwined crystals of quartz and feldspar in the texture known as graphic granite.[2]. Most pegmatites are granites with or without exotic minerals, but mafic pegmatites (gabbro, diorite) are known as well. (C) Modally graded crude igneous layering shown by alternate bands of mafic and felsic minerals in the granite. (B) Diorite is dismembered as xenoliths and partially assimilated by the intruding granite-leucogranite-pegmatite system. Is the Kimberlite rock defined as ultramafic rock or felsic rock? Pegmatite body size is on the order of magnitude of one to a few hundred meters. Coexistence of residual magma and a volatile-rich fluid (generally aqueous) promotes the partitioning and segregation of constituents, as well as the growth of very large crystals. Pegmatite. Pegmatite is a very coarse-grained igneous rock that has a grain size of 20 mm or more; such rocks are referred to as pegmatitic.. Water and fluxes generally reduce the melting point. Canadian Mineralogist Special Publication 10, 347 pp. FIGURE 2. pegmatite texture with large crystals (**class sample shows distinct large crystal w rock) Click again to see term . Most bodies of pegmatite are tabular, podlike (cigar-shaped), or irregular in form and range in size from single crystals of feldspar to dikes (tabular bodies injected in fissures) many tens of metres thick and more than a kilometre long; many are intimately associated with masses of fine-grained aplite. Ore minerals, chiefly sulfides and oxides, are widespread in pegmatites but rarely are abundant. Many granitic pegmatites contain unusual concentrations of the less-abundant elements. Economic lode concentrations generally occur in zoned pegmatite bodies (i.e., those within which two or more different rock types are systematically disposed). This ne-grained, dark-colored, igneous rock is most likely A. rhyolite B. diorite C. basalt D. gabbro page 2 Felsic … Felsic is a term that refers to silicate minerals, magmas, and rocks which are enriched in the lighter elements such as silica, oxygen, aluminum, sodium, and potassium. Worldwide, notable pegmatite occurrences are within the major cratons, and within greenschist-facies metamorphic belts. The word pegmatite derives from Homeric Greek, πήγνυμι (pegnymi), which means “to bind together”, in reference to the intertwined crystals of quartz and feldspar in the texture known as graphic granite.. 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. 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. felsic: Na-plagioclase, orthoclase, quartz, biotite, amphibole, muscovite: pegmatite: PHANERITIC TEXTURE (COARSE-GRAINED) Originates in deep intrusions, which cool and crystallize slowly underground. ... Coarse grained pegmatite dikes are associated with the granite intrusion of Black Elk Peak and are visibly lighter in color, thus explaining the light-colored streaks on the foreheads of the presidents. Material moves about very easily in these wet melts, and crystals can grow very large in a short time. In contrast the felsic rocks are typically light in color and enriched in aluminium and silicon along with potassium and sodium. The line in the pegmatite on the left indicates that the pegmatite is felsic, whereas the line in the pegmatite on the right indicates that the granite is intermediate O … intrusive. The term combines the words "feldspar" and "silica." Coexistence of residual magma and a volatile-rich fluid (generally aqueous) promotes the partitioning and segregation of constituents, as... Get a Britannica Premium subscription and gain access to exclusive content. Granite pegmatite (scale = 1cm) A light (felsic) igneous rock that is very coarse-grained. To be called a pegmatite, a rock should be composed almost entirely of crystals that are at least one centimeter in diameter. ... platy mineral in this mafic dike? felsic composition? The term “pegmatite” was first used by a French mineralogist René Haüy, but he used this term as a … Intruding the BUC, and in places gradational to the gabbros, is a suite of predominantly mafic, hornblende-bearing pegmatite dykes, which are the main focus of this study. Mafic is an adjective describing a silicate mineral or igneous rock which is rich in magnesium and iron.The term is a portmanteau, made up from "magnesium" and "ferric".. Mafic minerals are usually dark in color and have a specific gravity greater than 3.