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.) (a) Graphic granite. See under Granite. (b) More generally, a coarse granite occurring as vein material in other rocks.

• 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.