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Pegmatite Facts

Pegmatite Facts
A rock that forms during the final stage of a magma's crystallization is pegmatite, an igneous rock. They are exceptionally large crystals and may contain minerals that are not found in other types of rocks. It is a pegmatite if it is entirely composed of crystals, and it is at least one centimeter in dimeter. Its name has nothing to do with its mineral composition. Its composition is similar to granite with abundant feldspar, quartz, and mica. They may be called granite pegmatites indicating their mineral composition. Others may also be possible such as gabbro pegmatite, syenite pegmatite, and other plutonic rocks combined with pegmatite.
Interesting Pegmatite Facts:
Crystals of pegmatite grow large because of the extreme conditions of crystallization. Basically, the presence of residual water has allowed the magma to cool slowly to permit coarse crystal growth.
Complex pegmatites result because of the presence exotic volatiles such as chlorine, fluorine, and carbon dioxide.
The extreme conditions may produce crystals many feet in length and may weigh more than a ton.
An example of a very large crystal of spodumene is at the Etta Mine in South Dakota. It was 42 feet long, 5 feet in diameter, and yielded about 90 tons of spodumene.
Pegmatite also forms in small pockets along the margins of a batholith leading to pegmatite dikes. It will form from waters that separate from a magma in the late stages of crystallization.
The dikes and pockets are small in size, taking place underground following a dike or a small pocket. Pegmatites usually do not support large mining operations.
Rare elements concentrated in large crystals may make pegmatite a potential source of valuable ore. Pegmatite deposits may also contain gemstones, industrial minerals, and rare minerals.
Overall pegmatite rock has very few uses.
It has limited use as an architectural stone and is sometimes encountered in a dimension stone quarry that is producing granite.
Pegmatite, if sound and appealing, might be cut into slabs, polished, and used for building facades, countertops, tile, or other decorative stone products.
Pegmatite is most often sold commercially as a granite product.
The gemstones found in pegmatite include apatite, aquamarine, beryl, emerald, garnet, topaz, zircon, kunzite, and many others. Many are excellent-quality and are large crystals.
Pegmatite is the host rock for numerous mineral deposits and can be the commercial sources of beryllium, bismuth, tin, titanium, tungsten, niobium, and many other elements.
Large sheets of mica are often mined from pegmatite and used to make components electronic devices, circuit boards, optical filters, detector windows, and many other products.
Pegmatite is also used as a primary ingredient for making glass and ceramics, and as a filler for many other products.
Pegmatites occur in all parts of the world and are the most abundant in rocks of relatively great geologic age.


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