a form of igneous rock consisting of extremely coarse granite resulting from the crystallization of magma rich in rare elements
A coarsely crystalline igneous or plutonic rock composed primarily of feldspar and quartz, normally with muscovite and/or biotite mica. Often contains other minerals, which may be of economic importance. Pegmatite is chemically identical to granite, but has a much coarser crystal structure. Common colors are gray, white, and pink. Pegmatite is quarried for decorative stone and as a source of beryllium, columbium and tantalum when these are present. Gemstones of the quartz/silicate family may also be found in pegmatites.
graphic granite. See under Granite
more generally, a coarse granite occurring as vein material in other rocks
Origin: [From Gr. something fastened together, in allusion to the quartz and feldspar in graphic granite: cf. F. pegmatite. See Pegm.]
A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic. Most pegmatites are composed of quartz, feldspar and mica; in essence a granite. Rarer intermediate composition and mafic pegmatites containing amphibole, Ca-plagioclase feldspar, pyroxene and other minerals are known, found in recrystallised zones and apophyses associated with large layered intrusions. Crystal size is the most striking feature of pegmatites, with crystals usually over 5 cm in size. Individual crystals over 10 metres across have been found, and the world's largest crystal was found within a pegmatite. Similarly, crystal texture and form within pegmatitic rock may be taken to extreme size and perfection. 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. Perthite feldspar within a pegmatite often shows gigantic perthitic texture visible to the naked eye.
Chambers 20th Century Dictionary
peg′ma-tīt, n. coarsely crystallised granite.—adj. Pegmatit′ic.
The numerical value of pegmatite in Chaldean Numerology is: 8
The numerical value of pegmatite in Pythagorean Numerology is: 6
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