(peg'-ma-tite) A typically coarse-grained igneous rock formed through the crystallization of the very-last stages of magma typically granitic in composition that is enriched in water and other volatile elements (F, Cl) and, in some cases, highly incompatible elements (lithium, beryllium, boron, fluorine, niobium, tantalum, uranium, and the rare earth elements) that do not fit into the structures of minerals crystallized at higher temperatures and pressures. Although most pegmatites are composed of the common minerals feldspar, quartz, muscovite, and biotite, pegmatites rich in incompatible elements may also contain rare minerals. These incompatible elements make up a tiny fraction of the original magma, but because they are concentrated in the water-rich residual melt, they can occur in large enough quantities to produce large, well-formed crystals of beryl, chrysoberyl and euclase (beryllium), tourmaline (boron), topaz (fluorine), apatite (chlorine and fluorine), spodumene and lepidolite or lithium-rich pyroxene and mica, monazite (rare earth elements), tantalite (tantalum), and columbite (niobium).
Natural igneous rock formation consisting of a variety of granite usually characterized by coarse texture caused by crystallization from an exceptionally fluid magma rich in mineralizers containing rare elements
A very coarse grained igneous rock, normally of granitic composition. Typically forms during the final states of magma chamber crystallization when the high water content solutions allow rapid crystal growth.
Light-colored, very coarse-grained intrusive igneous rock, composed of feldspar, quartz, and micas; frequently can be seen in highway roadcuts as light-colored parallel and cross cutting veins and lenses in the metamorphic rock of the uplands; occasionally is a host for gem minerals. Pegmatite is a common and economically important rock type in Connecticut. It occurs in bodies too small to show on a state-scale geologic map. The Branchville area of western Connecticut and the Middletown area of eastern Connecticut have pegmatites of particular significance.
A very coarse-grained igneous rock, usually occurring in irregular dikes, lenses, or veins. Can be simple or complex. Pegmatite dikes are very important to the collector, as pockets filled with crystals are often present.
A very coarse-grained igneous rock, commonly with a granitic composition. Usually forms from molten rock rich in water or other volatiles that facilitate the growth of large crystals. Forms sills and dikes.
very coarse-grained igneous rock, with most grains interlocking and greater than one centimeter in diameter. The composition usually is granitic. Peg-matites represent the last and most water-rich portion of a magma to crystallize and hence contain high concentrations of minerals present only in trace amounts in typical granites. Often these minerals are rich in such elements as lithium, boron, fluorine, niobium, tantalum, uranium, and rare-earth elements like cerium.
a very coarse-grained igneous rock occurring in sills and dikes, and usually containing crystals of the common minerals found in granite, but sometimes containing rare minerals rich in such elements as lithium, uranium, and tantalum. [AHDOS