igneous
Quartz-rich pegmatite with smoky/amethyst quartz
Granitic pegmatite; predominantly SiO₂ quartz with feldspar and minor iron/manganese-bearing inclusions
AI-generated identification · may be incorrectHardness about 7 for quartz; white, cream, translucent gray, brown, and locally purple, with a vitreous to pearly luster. Coarse interlocking crystals, irregular fracture, and no obvious cleavage; feldspar portions are softer (Mohs 6).
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Physical properties
Hardness about 7 for quartz; white, cream, translucent gray, brown, and locally purple, with a vitreous to pearly luster. Coarse interlocking crystals, irregular fracture, and no obvious cleavage; feldspar portions are softer (Mohs 6).
Formation & geological history
Formed from the final, water-rich melt of a slowly cooling granitic intrusion, allowing unusually large quartz and feldspar crystals; commonly Precambrian to Phanerozoic in age depending on locality.
Uses & applications
Used mainly as a mineral-collecting specimen; pegmatites can also supply quartz, feldspar, mica, lithium, beryllium, and tantalum, while gem-quality quartz may be cut or polished.
Geological facts
The dark areas may be smoky quartz or iron/manganese-rich inclusions, and the purple patches may be amethyst; color alone cannot confirm either variety.
Field identification & locations
Identify by very coarse quartz-feldspar texture, glassy translucent quartz, and hardness sufficient to scratch ordinary glass. Common in granitic pegmatite districts worldwide, including Brazil, Madagascar, the United States, and Namibia.
