igneous
Granite-like pegmatitic rock
Coarse-grained granite or granitic pegmatite; likely quartz–feldspar–mica aggregate
AI-generated identification · may be incorrectHardness about 6–7 Mohs; mottled white, gray, and black with a granular texture and vitreous to pearly luster. Visible interlocking quartz and feldspar crystals suggest no strong cleavage as a whole, though feldspar and mica may cleave.
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Physical properties
Hardness about 6–7 Mohs; mottled white, gray, and black with a granular texture and vitreous to pearly luster. Visible interlocking quartz and feldspar crystals suggest no strong cleavage as a whole, though feldspar and mica may cleave.
Formation & geological history
Formed by slow cooling of silica-rich magma deep in the crust, allowing large crystals to grow; commonly Precambrian to Phanerozoic in age. The exact identification cannot be confirmed from a photograph alone.
Uses & applications
Used as dimension stone, countertops, aggregate, monuments, and decorative specimens; attractive pegmatites may contain collectible tourmaline, beryl, or large feldspar crystals. This small irregular specimen has modest commercial value.
Geological facts
The dark material may be biotite or amphibole, while the pale grains are probably quartz and feldspar. A glassy quartz grain, white feldspar, and reflective black mica are typical field clues.
Field identification & locations
Common in continental mountain belts and exposed plutons worldwide, including the United States, Canada, Brazil, India, and Scandinavia. Check for visible interlocking crystals, a light streak, lack of layering, and hardness sufficient to scratch glass.
