igneous
Granite, likely weathered biotite granite
Phaneritic intrusive igneous rock composed chiefly of quartz, feldspar, and biotite amphibole
AI-generated identification · may be incorrectMedium- to coarse-grained, speckled gray rock with black mica/amphibole and pale feldspar; typically Mohs 6–7, vitreous to dull luster, interlocking crystals, no cleavage as a rock, and specific gravity about 2.6–2.8.
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Physical properties
Medium- to coarse-grained, speckled gray rock with black mica/amphibole and pale feldspar; typically Mohs 6–7, vitreous to dull luster, interlocking crystals, no cleavage as a rock, and specific gravity about 2.6–2.8.
Formation & geological history
Formed when silica-rich magma cooled slowly deep underground, allowing visible crystals to grow; commonly Paleozoic to Precambrian in exposed continental crust, though age depends on locality.
Uses & applications
Widely used for building stone, countertops, monuments, paving, aggregate, and landscaping; attractive polished pieces have modest decorative and collector value.
Geological facts
The dark minerals are likely biotite or hornblende, while translucent grains are quartz. Its granular texture distinguishes it from fine-grained volcanic rocks such as rhyolite.
Field identification & locations
Identify it by visible interlocking quartz and feldspar grains, gray coloration, and black mica or amphibole flecks; common in continental mountain belts and glacial deposits. A precise identification requires a fresh surface or thin-section analysis.
