igneous
Quartz-rich pegmatitic rock, possibly tourmaline-bearing granite
Granitic pegmatite; predominantly quartz (SiO₂), feldspar, and mica, with possible schorl tourmaline
AI-generated identification · may be incorrectCoarse, irregular interlocking crystals; translucent gray-white quartz, pinkish weathered feldspar, dark mica or tourmaline, and a vitreous to pearly luster. Approximate hardness 6–7 Mohs; cleavage is weak in quartz but distinct in feldspar and mica; specific gravity about 2.6–2.8.
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Physical properties
Coarse, irregular interlocking crystals; translucent gray-white quartz, pinkish weathered feldspar, dark mica or tourmaline, and a vitreous to pearly luster. Approximate hardness 6–7 Mohs; cleavage is weak in quartz but distinct in feldspar and mica; specific gravity about 2.6–2.8.
Formation & geological history
Likely formed from the final, water-rich melts of a granite intrusion, allowing unusually large crystals to grow, commonly during Precambrian to Mesozoic intrusive events. The rough surface suggests weathering from a pegmatite vein or boulder.
Uses & applications
Used as a source of quartz, feldspar, mica, and occasionally lithium or rare-element minerals; attractive pieces are collected, while larger pegmatite material may be used decoratively.
Geological facts
Pegmatites can host spectacular crystals and rare minerals such as beryl, garnet, tourmaline, and spodumene. Exact identification requires a fresh surface, hardness testing, and ideally chemical or microscopic analysis.
Field identification & locations
Common in granitic terrains worldwide, including Brazil, Madagascar, the United States, and Scandinavia. Look for visibly coarse crystals, glassy quartz, blocky feldspar, and flaky mica; avoid assuming the dark grains are tourmaline without testing.
