igneous
Biotite-hornblende granite or granodiorite
Granitoid; chiefly quartz (SiO₂), feldspar, biotite, and hornblende
AI-generated identification · may be incorrectMedium- to coarse-grained, speckled gray-brown rock with pale feldspar/quartz and dark ferromagnesian minerals; hardness about 6–7 Mohs, vitreous to pearly luster, interlocking crystals, and no obvious cleavage as a whole.
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Physical properties
Medium- to coarse-grained, speckled gray-brown rock with pale feldspar/quartz and dark ferromagnesian minerals; hardness about 6–7 Mohs, vitreous to pearly luster, interlocking crystals, and no obvious cleavage as a whole.
Formation & geological history
A plutonic igneous rock formed when silica-rich magma cooled slowly deep underground, allowing visible crystals to grow; commonly Precambrian to Phanerozoic in age, depending on locality.
Uses & applications
Used as crushed stone, aggregate, building stone, monuments, and countertops; attractive polished pieces have modest lapidary and collecting value.
Geological facts
The specimen’s uneven granular texture and contrasting light and dark minerals are typical of granitoids, though a photograph cannot reliably distinguish granite from granodiorite or gneiss.
Field identification & locations
Common in continental mountain belts and exposed shields worldwide. Identify it by visible interlocking quartz/feldspar grains and dark mica or amphibole; gneiss would show stronger mineral banding, while basalt is much finer-grained.
