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The Collaborative International Dictionary

Pegmatite \Peg"ma*tite\, n. [From Gr. ? something fastened together, in allusion to the quartz and feldspar in graphic granite: cf. F. pegmatite. See Pegm.] (Min.)

  1. Graphic granite. See under Granite.

  2. More generally, a coarse granite occurring as vein material in other rocks.


n. 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. gemstone of the quartz/silicate family may also be found in pegmatites.


n. a form of igneous rock consisting of extremely coarse granite resulting from the crystallization of magma rich in rare elements


A pegmatite is a holocrystalline, intrusive igneous rock composed of interlocking phaneritic crystals usually larger than 2.5 cm in size (1 inch); such rocks are referred to as pegmatitic.

The word pegmatite derives from Homeric Greek, πεγνυμι (pegnymi), which means “to bind together”, in reference to the intertwined crystals of quartz and feldspar in the texture known as graphic granite.

Most pegmatites are composed of quartz, feldspar and mica, having a similar basic composition as granite. 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.

Crystal size is the most striking feature of pegmatites, with crystals usually over 5 cm in size. Individual crystals over long have been found, and many of the world's largest crystals were found within pegmatites. These include, spodumene, microcline, beryl, and tourmaline.

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.

Usage examples of "pegmatite".

USE-trained geologists map the pegmatite fields of Sweden, the USE and Sweden will presumably import muscovite mica from Russia, or possibly, India.

But the whole area was overlain by thousands of feet of Miocene lava flows and of course it was geological insanity to look there for a pegmatite vein.

The rock was stained red, with veins of white quartzite and schist, the first sign of an underlying pegmatite structure.

They consist chiefly of granulitic quartzose schists and felspathic gneisses, permeated in places by strings and veins of pegmatite.