igneous
Mica-rich granite or granitic pegmatite
Quartz–feldspar–mica aggregate, commonly biotite granite or muscovite-bearing pegmatite
AI-generated identification · may be incorrectCoarse-grained, speckled gray, white, and brown material with glassy quartz, pale feldspar, and reflective mica. Quartz hardness is 7, feldspar about 6, and mica 2–3; luster ranges from vitreous to pearly, with mica showing perfect basal cleavage.
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Physical properties
Coarse-grained, speckled gray, white, and brown material with glassy quartz, pale feldspar, and reflective mica. Quartz hardness is 7, feldspar about 6, and mica 2–3; luster ranges from vitreous to pearly, with mica showing perfect basal cleavage.
Formation & geological history
Formed when silica-rich magma cooled slowly underground, allowing large interlocking crystals to grow; pegmatitic varieties formed from late-stage, water-rich melt. Most examples are Paleozoic to Precambrian, though age depends on locality.
Uses & applications
Used as building stone, aggregate, countertops, and decorative material; attractive crystal-rich pieces are collected, while mica may have limited industrial value.
Geological facts
The bright flakes are likely muscovite or biotite, which split into thin elastic sheets. A fresh broken surface commonly reveals interlocking crystals rather than layers or fossils.
Field identification & locations
Common in continental mountain belts and granite outcrops worldwide. Identify it by coarse interlocking quartz and feldspar plus reflective mica; a steel knife generally scratches feldspar but not quartz.
