igneous
Porphyritic granitic pegmatite
Granitic pegmatite, composed chiefly of quartz, feldspar, and mica
AI-generated identification · may be incorrectCoarse-grained, light gray to cream matrix with glassy quartz, white feldspar, reflective mica, and scattered dark accessory minerals; typical hardness 6–7, vitreous to pearly luster, and interlocking crystalline texture. The rounded cavity-like feature may be a weathered feldspar or miarolitic pocket.
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Physical properties
Coarse-grained, light gray to cream matrix with glassy quartz, white feldspar, reflective mica, and scattered dark accessory minerals; typical hardness 6–7, vitreous to pearly luster, and interlocking crystalline texture. The rounded cavity-like feature may be a weathered feldspar or miarolitic pocket.
Formation & geological history
Formed when water-rich granitic magma cooled slowly near the margins of an intrusion, allowing unusually large crystals to grow; commonly Precambrian to Mesozoic, depending on locality. Weathering may have softened or dissolved feldspar, producing cavities.
Uses & applications
Used as decorative stone, aggregate, and a source of quartz, feldspar, mica, and occasional rare minerals or gemstones; attractive specimens are collected rather than used industrially.
Geological facts
Pegmatites can host tourmaline, beryl, garnet, lithium minerals, and large quartz crystals. Their extreme crystal size results from volatile-rich residual magma and prolonged cooling.
Field identification & locations
Identify it by its very coarse interlocking crystals, pale quartz-feldspar groundmass, mica flakes, and occasional cavities; it is commonly found in granitic terrains and pegmatite dikes worldwide. A precise locality or tests for hardness and streak would be needed for a narrower identification.
