igneous
Mica-rich granite (likely biotite granite)
Biotite granite; mainly quartz (SiO₂), alkali/feldspar, and biotite mica
AI-generated identification · may be incorrectCoarse-grained, light gray to white rock with conspicuous black, platy biotite; quartz is glassy and feldspar is blocky. Hardness is roughly 6–7 Mohs, with low foliation, granular texture, and no obvious cleavage as a whole.
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Physical properties
Coarse-grained, light gray to white rock with conspicuous black, platy biotite; quartz is glassy and feldspar is blocky. Hardness is roughly 6–7 Mohs, with low foliation, granular texture, and no obvious cleavage as a whole.
Formation & geological history
Intrusive igneous rock formed when silica-rich magma slowly crystallized deep underground, allowing large crystals to grow; its exact geological age cannot be determined from the image and may range from Precambrian to recent.
Uses & applications
Used as crushed stone, dimension stone, countertops, monuments, aggregate, and landscaping material; rounded pieces are also collected as geological specimens.
Geological facts
The black mineral is most likely biotite, though hornblende is possible; white areas are feldspar and translucent grains are quartz. The rounded shape appears to result from weathering or tumbling rather than its original underground form.
Field identification & locations
Identify it by its coarse interlocking grains, abundant pale quartz/feldspar, and shiny black mica flakes; it is common in continental mountain belts and exposed plutons worldwide, including North America, Europe, and India.
