igneous
Pegmatite (Granitic Pegmatite with Quartz, Mica, and Tourmaline/Biotite)
Pegmatite
Hardness 6-7 on Mohs scale. Light gray, translucent quartz mixed with silvery flaky muscovite mica and dark black inclusions (tourmaline or biotite). Vitreous to pearly luster with coarse-grained, irregular texture.
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Physical properties
Hardness 6-7 on Mohs scale. Light gray, translucent quartz mixed with silvery flaky muscovite mica and dark black inclusions (tourmaline or biotite). Vitreous to pearly luster with coarse-grained, irregular texture.
Formation & geological history
Formed during the final stages of a magma body's crystallization, where water-rich fluids allow extremely large crystals to grow rapidly. Commonly found in continental crust and metamorphic terranes.
Uses & applications
Used as a major source of rare earth minerals, lithium, mica, quartz, feldspar, and gemstones. River-rounded pebbles are collected for lapidary interest.
Geological facts
Pegmatites host some of the largest mineral crystals ever discovered on Earth. They are often targeted by gem hunters for tourmaline, beryl, and topaz.
Field identification & locations
Look for exceptionally large mineral grains (quartz, feldspar, mica) and dark tourmaline or biotite inclusions. Commonly found in glacial deposits, riverbeds, and mountainous granitic regions.
