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Most pegmatites consist of granite that contains quartz, feldspar and mica. Pegmatites are important because they often contain other rare earth minerals and gemstones, such as aquamarine, tourmaline, topaz, fluorite, apatite, tin, and tungsten, among others. Crystals over 10 meters across have been found.
Granitic pegmatites, boron-granitic pegmatites, lithia pegmatites, and boron-lithia pegmatites exist.
Pegmatites are formed from magma that has cooled very slowly, usually deep underground. When the magma cools slowly underground, and there is an opportunity for the various chemical components of the magma to precipitate out and form crystalThis article is about the form of solid matter. For other uses of this word, see Crystal (disambiguation . Insulin Crystals A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extends. A good example of a rock formed this way is common granite. If you look at granite, you will see that it is made up of small crystals of feldspar, quartz and mica. When magma comes to the surface, such as with a volcanoThis article is about volcanoes geology. For the action movie see: Volcano (movie). A volcano (plural, volcanoes) is a geological landform (usually a mountain) where magma (rock of the earth's interior made molten or liquid by high pressure and temperatur or lava vent, the magma cools very rapidly and produces glassy or very fine-grained rocks like obsidianObsidian is a type of naturally occurring glass, produced from volcanoes when the right kind of lava cools rapidly, e. by flowing into a body of water. It consists mainly of SiO (silicon dioxide), 70% or more. Obsidian is mineral-like, but not a true mine, pumiceobsidian, below that is pumice and in lower right hand color is rhyolite (light color). Pumice is a light, porous type of pyroclastic igneous rock. It is formed during explosive volcanic eruptions when liquid lava is ejected into the air as a froth contai or rhyoliteRhyolite is an igneous, volcanic ( extrusive) rock, of felsic composition, with aphanitic to porphyritic texture. Mineral assembly is usually quartz, alkali feldspar and plagioclase (in a ratio > 1:2). Biotite and pyroxene are common accessory minerals..
As result of their slow cooling, pegmatites can have very large crystals, sometimes many feet in length. The long cooling time can also concentrate rarer elements in the pegmatites. Consequently, it is not uncommon to find rare minerals and even gem stones in pegmatites. For example, beautiful crystals of aquamarines and topaz can be found in pegmatites in the mountains of ColoradoThere are also three Colorado Rivers: two in the United States and one in Argentina. Colorado is a state in the western United States. The name of Colorado came from the Spanish word "colorado" which means "reddish color". The name comes from the Colorado and IdahoIdaho ( In Detail) (Full size) State nickname: Gem State Other U. States Capital Boise Largest City Boise Governor Dirk Kempthorne Area Total Land Water % water Ranked 14th 216,632 kmē214,499 kmē 2,133 kmē1% Population Total ( 2000) Density Ranked 39th1,2. Pegmatites are also a source for rare earth minerals such as columbite and tantalite .
Pegmatites tend to form veins and thick bands in granites. They can also form pockets that can contain beautifully formed crystals. This is because the crystals are free to grow in the empty space of the pocket without crowding or distortion.
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