pegmatite

A coarse-grained granite, sometimes rich in rare elements such as uranium, tungsten, and tantalum.

Coarsely crystallized granite. Also called granitel, granitelle.

Graphic granite. See under granite.

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.

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