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 meters 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...'
Contributions by Vsmith, Wilson44691, and 18.104.22.168.