igneous
Granitic Pegmatite
Granitic Pegmatite (principally Quartz, Feldspar, and Mica)
Hardness: 6-7 (Mohs scale), Color: White, cream, and grey with silvery flecks, Luster: Vitreous to pearly, Crystal Structure: Macro-crystalline (very large crystals), Cleavage: Perfect in feldspar and mica components, Specific Gravity: 2.5-2.8
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Physical properties
Hardness: 6-7 (Mohs scale), Color: White, cream, and grey with silvery flecks, Luster: Vitreous to pearly, Crystal Structure: Macro-crystalline (very large crystals), Cleavage: Perfect in feldspar and mica components, Specific Gravity: 2.5-2.8
Formation & geological history
Formed during the final stages of a magma's crystallization when high water content allows for the growth of exceptionally large crystals. Typically found in dikes or veins within plutonic bodies.
Uses & applications
Source of rare earth elements, industrial minerals like feldspar and quartz, and occasionally gemstones like tourmaline or beryl. Mostly used for decorative displays or geological study when unprocessed.
Geological facts
Pegmatites are famous for containing the largest crystals ever found on Earth; some spodumene crystals in pegmatites have reached lengths of nearly 50 feet.
Field identification & locations
Identify by the exceptionally large grain size compared to standard granite. Look for the silvery, reflective flakes of mica. Common in shield areas like the Appalachians or the Rockies.
