Pegmatitic

Pegmatitic refers to the texture of certain igneous rocks in which crystals are exceptionally large, often several centimeters to decimeters or more in size. Pegmatitic rocks, usually granitoid in composition, are dominated by coarse interlocking crystals of feldspar and quartz and frequently contain conspicuously large crystals of feldspar, mica, or quartz, along with rare minerals. The rocks commonly occur as dikes, veins, or satellite bodies within granitic intrusions.

Formation: The pegmatitic texture forms during the final stages of granitic crystallization when the remaining melt becomes highly enriched in volatiles (water, fluorine, boron) and incompatible elements. This chemical environment promotes rapid growth of large crystals in pockets or along fractures, often at the expense of finer-grained surrounding material. Cooling is typically slow, and the presence of hydrothermal fluids enhances mineral diversity.

Mineralogy and deposits: Pegmatites host a suite of accessory minerals such as tourmaline, spodumene, beryl, cassiterite, columbite-tantalite, zircon, and rare earth–bearing minerals. Because of their concentrated lithium, beryllium, tantalum, niobium, cesium, and rare earth elements, pegmatites are important ore sources. They also yield gem-quality crystals of tourmaline, aquamarine, and emerald in some occurrences.

Occurrence: Pegmatites are worldwide, commonly linked with granitic plutons and batholiths. They form at late stages of crustal differentiation and are especially abundant in shield areas and crustal terranes with substantial granitic magmatism.