Classification of rocks, minerals, and magma based on the silica content present in them defines them as either mafic or felsic. (C) Modally graded crude igneous layering shown by alternate bands of mafic and felsic minerals in the granite. Pegmatites may be mined because of their high content of feldspars, clay (if weathered), mica, or many metal-bearing minerals. One pegmatite intrusive dike is more mafic than its host gabbro, suggesting that this pegmatite melt did not form in place. It is felsic because it is lightly colored. Intermediate, between that of mafic gabbro and felsic granite. A sample of the mineral with usual composition may be easily identifiable, but it is actually a mineral group because there are numerous possible replacements in the crystal lattice which gives rise to several end-members with different compositions. The mafic magmas are somewhat more viscous than the ultramafic magmas, but they are still fairly fluid. Pegmatites are the primary source of lithium either as spodumene, lithiophyllite or usually from lepidolite. ... (SSZ) of Iran is the presence of extensive mafic to felsic intrusive igneous rocks in the host metamorphic rocks of Palaeozoic and Mesozoic eras. In geology, felsic is an adjective describing igneous rocks that are relatively rich in elements that form feldspar and quartz. in advance, thanks very much ....i would appreciate the help ^_^ The felsic minerals include quartz, tridymite, cristobalite, feldspars (plagioclase and alkali feldspar), feldspathoids (nepheline and leucite), muscovite, and corundum. Pegmatite. The term “pegmatite” was first used by a French mineralogist René Haüy, but he used this term as a … Some are segregations within much larger bodies of intrusive igneous rocks, others are distributed in the rocks that surround such bodies, and still others are not recognizably associated with igneous rocks. Some skarns associated with granites also tend to host pegmatites. Mafic or hybrid magmas inject into felsic magma at low volume fraction (<0.35) of crystals and form the rounded to elongated microgranular enclaves in the Ladakh Batholith. 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.. ... platy mineral in this mafic dike? Pegmatites are little different from the common igneous rocks in major elements of bulk composition, and they range from felsic to mafic (silica-rich to silica-poor); granitic and syenitic types are … 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). Basalt is a mafic extrusive igneous rock formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. Bismuth, molybdenum and tin have been won from pegmatite, but this is not yet an important source of these metals. A light (felsic) igneous rock that is very coarse-grained. Economic lode concentrations generally occur in zoned pegmatite bodies (i.e., those within which two or more different rock types are systematically disposed). DIORITE - phaneritic rock (large crystals) of both mafic and felsic minerals. 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. Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... Alkaline pegmatite, with blue corundum crystals, Rio de Janeiro, Brazil. 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. The most common felsic rock is granite, which represents the purified end product of the earth’s internal differentiation process. Igneous rock - Igneous rock - Mineralogical components: The major mineralogical components of igneous rocks can be divided into two groups: felsic (from feldspar and silica) and mafic (from magnesium and ferrous iron). Pegmatite body size is on the order of magnitude of one to a few hundred meters. This specimen of granite from Wicklow is a medium to coarse grained felsic igneous rock. 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. (C) Modally graded crude igneous layering shown by alternate bands of mafic and felsic minerals in the granite. Felsic refers to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. Granite pegmatite (scale = 1cm) (1998). © Instituto del Corazón San Pablo. GEOL A105L Igneous Rock Identification Lab Name: Dexter Doan Terms to know prior to completing this lab: intrusive, extrusive, plutonic, volcanic, texture, composition, mafic, felsic, intermediate, aphanitic, phaneritic, vesicular, porphyritic, pegmatitic, glassy. DIORITE - phaneritic rock (large crystals) of both mafic and felsic minerals. In geology, felsic is an adjective describing igneous rocks that are relatively rich in elements that form feldspar and quartz. Felsic minerals are usually light in color and have specific gravities less than 3. Many granitic pegmatites contain unusual concentrations of the less-abundant elements. Pegmatites occur in all parts of the world and are most abundant in rocks of relatively great geologic age. 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. A limited amount of chemical data for gabbros from the BUC was reported by Kerr et al. Pegmatite is also a source of gems like beryl, tourmaline, zircon, etc. Pegmatites are little different from the common igneous rocks in major elements of bulk composition, and they range from felsic to mafic (silica-rich to silica … This suggests that these pegmatites formed in place and in equilibrium with their gabbro host. Rocks with similar texture to pegmatites are called pegmatitic. Tap again to see term . The term combines the words "feldspar" and "silica." Ring in the new year with a Britannica Membership, This article was most recently revised and updated by, https://www.britannica.com/science/pegmatite, Victoria and Albert Museum - Classical Ballet, College of Natural Resources - Pegmatites. Often, bulk samples of some 50–60 kg of rock must be crushed to obtain a meaningful and repeatable result. Felsic refers to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. During the rock cycle, the most volatile components tend towards the felsic rocks. Additionally, they contain somewhat more gas than do the ultramafic magmas, but not nearly so much as the felsic magmas. The 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. Pegmatite bodies are usually of minor size compared to typical intrusive rock bodies. Quartz and alkali feldspars are the essential constituents; the most common varietal and accessory minerals are muscovite, biotite, apatite, garnet, and tourmaline. A pegmatite is an igneous rock, formed underground, with interlocking crystals usually larger than 2.5 cm in size (1 in). Syenite pegmatites are quartz depleted and contain large feldspathoid crystals instead.