Very coarse-grained, igneous rock, usually of granitic composition, in which the individual crystals are at least 2.5 cm long. The crystals are often more than 1 m in length, and may be far larger. Crystallization occurs at a late stage, when the magma is enriched in volatiles and trace elements. Pegmatites may concentrate some rare elements (lithium, boron, fluorine, tantalum, niobium, rare-earth elements, and uranium) to economic proportions.