igneous
Pegmatite (Granitic Pegmatite)
Pegmatite (Quartz + Potassium Feldspar + Mica)
Hardness 6-7 on Mohs scale. Coarse-grained phaneritic or pegmatitic texture with large interlocking crystals of pink-to-peach orthoclase feldspar, gray glassy quartz, and minor mica/biotite. Luster ranges from vitreous to dull.
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Physical properties
Hardness 6-7 on Mohs scale. Coarse-grained phaneritic or pegmatitic texture with large interlocking crystals of pink-to-peach orthoclase feldspar, gray glassy quartz, and minor mica/biotite. Luster ranges from vitreous to dull.
Formation & geological history
Formed during the final stages of a magma chamber's crystallization, where water-rich fluids allow extremely large mineral crystals to grow rapidly at depth beneath the Earth's crust.
Uses & applications
Used as source rock for industrial feldspar, quartz, and mica. Also mined for rare-earth metals and gemstone minerals like beryl, tourmaline, and topaz found in pockets. Common as decorative garden stone.
Geological facts
Pegmatites contain some of the largest crystals ever found on Earth, occasionally reaching tens of feet in length. They are notorious among collectors for hosting rare, exotic gem minerals.
Field identification & locations
Identified by its distinctly large, visible crystal grains (over 1 cm in size), predominantly composed of pinkish feldspar and translucent gray quartz. Commonly found in continental crust areas and mountain belts.
