igneous
Quartz-bearing pegmatitic rock with feldspar
Granitic pegmatite; chiefly quartz (SiO₂), feldspar, and mica
AI-generated identification · may be incorrectCoarse-grained, gray to white rock with glassy to pearly luster; the rounded cream-white crystal is likely feldspar or quartz. Hardness is approximately 6–7 for quartz and 6–6.5 for feldspar; crystals are generally irregular to blocky, with feldspar cleavage.
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Physical properties
Coarse-grained, gray to white rock with glassy to pearly luster; the rounded cream-white crystal is likely feldspar or quartz. Hardness is approximately 6–7 for quartz and 6–6.5 for feldspar; crystals are generally irregular to blocky, with feldspar cleavage.
Formation & geological history
Formed when water-rich granitic magma cooled slowly, allowing exceptionally large crystals to grow, typically during Precambrian to Phanerozoic intrusive events. Exact identification and age require thin-section or chemical analysis.
Uses & applications
Used as a source of quartz, feldspar, mica, and occasionally rare minerals or gemstones; attractive specimens are collected, while ordinary pegmatite has limited construction use.
Geological facts
Pegmatites commonly host tourmaline, beryl, garnet, lithium minerals, and sometimes tantalum or rare-earth minerals. The apparent rounded crystal may also be a weathered feldspar or a different mineral inclusion.
Field identification & locations
Identify by visibly oversized interlocking crystals and contrasting quartz-feldspar-mica grains; common in granitic terrains and exposed veins worldwide. A diagnostic hardness, streak, cleavage, and close-up crystal inspection would improve certainty.
