igneous
Biotite-rich granite or granitic gneiss
Granite; quartz + feldspar + biotite mica, possibly weakly gneissic
AI-generated identification · may be incorrectCoarse-grained, brown-gray rock with pale quartz/feldspar and dark, shiny biotite flakes; Mohs hardness about 6–7, vitreous to pearly luster, interlocking crystals, and no prominent cleavage as a whole. The irregular dark-light texture may indicate mild metamorphic banding, but the image is insufficient for certainty.
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Physical properties
Coarse-grained, brown-gray rock with pale quartz/feldspar and dark, shiny biotite flakes; Mohs hardness about 6–7, vitreous to pearly luster, interlocking crystals, and no prominent cleavage as a whole. The irregular dark-light texture may indicate mild metamorphic banding, but the image is insufficient for certainty.
Formation & geological history
Crystallized slowly from silica-rich magma deep in the continental crust, commonly during Precambrian to Phanerozoic mountain-building events; if gneissic, it was later subjected to high heat and pressure.
Uses & applications
Used as dimension stone, countertops, monuments, aggregate, and landscaping rock; attractive pieces may be collected as hand specimens.
Geological facts
Granite is identified by visible quartz, feldspar, and mica crystals rather than the fine texture of basalt. Biotite commonly gives the rock its black reflective flecks.
Field identification & locations
Common worldwide in continental mountain belts, including India, Scandinavia, Canada, and the United States. A fresh broken surface, acid test for carbonate, and hand lens showing quartz and feldspar help confirm it; value is typically $5–$25 for an ordinary specimen, or $30–$100+ if unusually attractive or locality-labeled.
