igneous
Pegmatite
Pegmatitic Granite containing Quartz, Feldspar, and Schorl
Hardness: 6-7 (Mohs scale), Color: White, grey, and black mottled, Luster: Vitreous to pearly, Crystal structure: Very coarse-grained phaneritic, Cleavage: Perfect in two directions for feldspar, none for quartz
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Physical properties
Hardness: 6-7 (Mohs scale), Color: White, grey, and black mottled, Luster: Vitreous to pearly, Crystal structure: Very coarse-grained phaneritic, Cleavage: Perfect in two directions for feldspar, none for quartz
Formation & geological history
Formed during the final stages of a magma's crystallization, where high water content allows for the growth of exceptionally large crystals. Typically found in plutonic environments.
Uses & applications
Source of rare earth elements, industrial quartz and feldspar, and occasional high-quality gemstone specimens like tourmaline.
Geological facts
Crystals in pegmatites can grow to massive sizes; some feldspar crystals in pegmatites have been recorded at over 10 meters in length.
Field identification & locations
Identify in the field by unusually large crystal sizes compared to surrounding granite. Often found in dikes or veins cutting across other igneous or metamorphic rocks.
