igneous
Biotite-rich granite or granitic gneiss
Quartz–feldspar–biotite granite; possibly weakly foliated gneiss
AI-generated identification · may be incorrectCoarse-grained, gray-and-white rock with dark reflective biotite mica; likely quartz and feldspar. Hardness is approximately 6–7 overall, with vitreous quartz, blocky feldspar, and mica cleavage; specific gravity about 2.6–2.8.
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Physical properties
Coarse-grained, gray-and-white rock with dark reflective biotite mica; likely quartz and feldspar. Hardness is approximately 6–7 overall, with vitreous quartz, blocky feldspar, and mica cleavage; specific gravity about 2.6–2.8.
Formation & geological history
Formed when silica-rich magma crystallized slowly underground, commonly during Precambrian to younger continental-crust events; any foliation would indicate later metamorphism. The image alone cannot establish an exact age or composition.
Uses & applications
Common granite is used as crushed aggregate, building stone, countertops, monuments, and decorative material. This small fragment has negligible commercial value.
Geological facts
The glittering dark flakes are likely biotite, which splits into thin elastic sheets. Gray quartz and pale feldspar are typical of felsic continental rocks.
Field identification & locations
Identify it by its visible interlocking crystals, light quartz/feldspar matrix, and black mica flakes; it is not glassy or vesicular. Common worldwide, especially in continental shields and mountain belts.
