igneous
Pegmatitic granite with dark mica/amphibole
Coarse-grained felsic intrusive rock; chiefly quartz, alkali feldspar, plagioclase, and biotite/hornblende
AI-generated identification · may be incorrectHardness about 6–7; pale pink-white, gray, and black, with a coarse interlocking crystal texture and vitreous-to-pearly luster. Quartz has no cleavage, feldspar shows two cleavages, and dark minerals are likely biotite or hornblende; specific gravity is roughly 2.6–2.8.
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Physical properties
Hardness about 6–7; pale pink-white, gray, and black, with a coarse interlocking crystal texture and vitreous-to-pearly luster. Quartz has no cleavage, feldspar shows two cleavages, and dark minerals are likely biotite or hornblende; specific gravity is roughly 2.6–2.8.
Formation & geological history
Slow crystallization of silica-rich magma deep underground produced the large visible crystals, likely during a Precambrian to Phanerozoic intrusive event. Weathering has rounded and roughened the specimen.
Uses & applications
Used as dimension stone, countertops, aggregate, and monuments; attractive pieces are sold as teaching or display specimens rather than jewelry material.
Geological facts
The unusually large crystals suggest a pegmatitic phase or coarse granite. A glassy gray grain is likely quartz, while pink/tan grains are feldspar and black grains are mica or amphibole.
Field identification & locations
Common in continental shields, mountain belts, and granite pegmatite districts worldwide; notable sources include Maine, North Carolina, South Dakota, Brazil, and Scandinavia. Confirm with a hand lens and streak, and test hardness against steel or glass.
