igneous
Pegmatite
Granitic pegmatite, likely quartz and feldspar with dark mica (biotite)
AI-generated identification · may be incorrectCoarse, irregularly intergrown crystals; pale translucent quartz/feldspar with dark, shiny mica. Quartz hardness 7, feldspar 6, and biotite 2.5–3 on the Mohs scale; exact mineral identification is uncertain from the photo.
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Physical properties
Coarse, irregularly intergrown crystals; pale translucent quartz/feldspar with dark, shiny mica. Quartz hardness 7, feldspar 6, and biotite 2.5–3 on the Mohs scale; exact mineral identification is uncertain from the photo.
Formation & geological history
Pegmatite forms when water-rich, silica-rich magma cools slowly in veins or dikes, allowing unusually large crystals to grow. Most pegmatites formed during ancient episodes of continental crust formation, commonly hundreds of millions to billions of years ago.
Uses & applications
Pegmatites are sources of feldspar, quartz, mica, and sometimes lithium, tantalum, or gemstones; small ordinary pieces are mainly collected as geological specimens.
Geological facts
Pegmatites can contain crystals ranging from millimeters to many meters long and are important sources of rare elements and minerals.
Field identification & locations
Look for a coarse, interlocking texture with conspicuously large crystals, often quartz, feldspar, and mica. Common in granitic regions worldwide; confirm minerals with hardness and streak tests, since the photo alone cannot establish the exact identification.
