Pegmatite

Pegmatite is a very coarse-grained igneous rock having a grain size of 20 mm or more; such rocks are referred to as pegmatitic.

Most pegmatites are granite with quartz, feldspar, and mica. Pegmatites are important because they often contain other rare earth minerals and gemstones, such as aquamarine, tourmaline, topaz, fluorite, apatite, tin, and tungsten, among others.

Granitic pegmatites, boron granitic pegmatites, lithia pegmatites, and boron lithia pegmatites exist.