igneous
Quartz-rich pegmatite (likely graphic granite)
Granitic pegmatite; chiefly quartz (SiO₂), feldspar, and mica, with possible iron-oxide staining
AI-generated identification · may be incorrectCoarse-grained, pale gray to white, with glassy-to-pearly luster and irregular fractures; individual crystals appear centimeter-scale. Quartz hardness is 7 Mohs, feldspar 6–6.5, and mica 2–3; precise identification would benefit from a fresh surface and tests.
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Physical properties
Coarse-grained, pale gray to white, with glassy-to-pearly luster and irregular fractures; individual crystals appear centimeter-scale. Quartz hardness is 7 Mohs, feldspar 6–6.5, and mica 2–3; precise identification would benefit from a fresh surface and tests.
Formation & geological history
Forms when the final, water-rich melt from a granitic magma crystallizes slowly in veins or pockets, commonly during Precambrian to Phanerozoic mountain-building. The rusty brown areas likely represent weathered sulfide or iron-bearing minerals.
Uses & applications
Used as a source of feldspar, quartz, and mica, as dimension stone or aggregate, and commonly collected as a specimen; gem-quality pockets may contain tourmaline, beryl, or garnet.
Geological facts
Pegmatites can produce exceptionally large crystals because volatile-rich melt allows rapid ion transport during late crystallization.
Field identification & locations
Look for very coarse interlocking quartz and feldspar, mica flakes, and a sugary or glassy fracture; it should not fizz in dilute acid. Common in granitic terrains worldwide, especially Brazil, Madagascar, the United States, and Scandinavia.
