igneous
Pegmatitic mica-rich granite
Granitic pegmatite, composed mainly of quartz, feldspar, and biotite/muscovite mica
AI-generated identification · may be incorrectCoarse-grained, uneven texture with translucent gray quartz, pale feldspar, and black/brown mica; vitreous quartz luster, feldspar cleavage, mica sheet cleavage; hardness about 2–7 Mohs, depending on mineral.
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Physical properties
Coarse-grained, uneven texture with translucent gray quartz, pale feldspar, and black/brown mica; vitreous quartz luster, feldspar cleavage, mica sheet cleavage; hardness about 2–7 Mohs, depending on mineral.
Formation & geological history
Forms when silica-rich magma cools slowly, allowing exceptionally large crystals to grow in late-stage veins or pockets. Most examples are Precambrian to Phanerozoic, depending on the host intrusion.
Uses & applications
Used mainly as a collector specimen; pegmatites may also host feldspar, mica, quartz, lithium minerals, beryl, and tourmaline. Unexceptional material has little construction value.
Geological facts
The large interlocking crystals and sparkly platy mica are characteristic of pegmatitic texture. Dark patches may be biotite or other accessory minerals, while rusty areas commonly reflect weathered iron-bearing minerals.
Field identification & locations
Common in granitic terrains worldwide, including Brazil, the United States, Canada, Madagascar, and India. Field identification relies on very coarse crystals, visible quartz and feldspar, and flaky mica; exact identification requires testing or microscopy.
