igneous
Quartz-rich pegmatite fragment
Granite-family pegmatite; chiefly quartz (SiO₂), feldspar, and black mica (biotite)
AI-generated identification · may be incorrectCoarse, interlocking crystals with white/translucent quartz or feldspar and black biotite; vitreous to pearly luster, uneven fracture, no obvious cleavage in quartz. Hardness is approximately 6–7 for quartz and feldspar, while biotite is about 2.5–3.
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Physical properties
Coarse, interlocking crystals with white/translucent quartz or feldspar and black biotite; vitreous to pearly luster, uneven fracture, no obvious cleavage in quartz. Hardness is approximately 6–7 for quartz and feldspar, while biotite is about 2.5–3.
Formation & geological history
Formed when water-rich magma cooled slowly in a shallow igneous intrusion, allowing unusually large crystals to grow; typically Precambrian to Phanerozoic, depending on locality.
Uses & applications
Used as an aggregate or source of quartz and feldspar; attractive pieces are collected, though this small specimen has little commercial value.
Geological facts
Pegmatites can host tourmaline, beryl, garnet, lithium minerals, and rare-earth minerals. The apparent dark flakes are likely biotite mica.
Field identification & locations
Identify by coarse crystal size, pale quartz/feldspar, and easily splitting black mica; quartz scratches glass, while feldspar commonly shows cleavage. Common in granitic terrains worldwide.
