igneous
Feldspar-rich granite or granitic gneiss with dark inclusion
Granite, likely quartz–feldspar–mica rock; dark area may be biotite-rich enclave or weathered mafic inclusion
AI-generated identification · may be incorrectLight gray, coarse-grained, granular texture with pale feldspar/quartz and a dark gray-black patch. Typical hardness is about 6–7 Mohs, glassy to dull luster, interlocking crystals, and no obvious cleavage on the weathered surface.
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Physical properties
Light gray, coarse-grained, granular texture with pale feldspar/quartz and a dark gray-black patch. Typical hardness is about 6–7 Mohs, glassy to dull luster, interlocking crystals, and no obvious cleavage on the weathered surface.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep in the crust, generally during Precambrian to younger continental events; the dark patch likely formed as a mafic xenolith or biotite-rich segregation incorporated into the magma.
Uses & applications
Commonly used as crushed stone, aggregate, building stone, countertops, monuments, and architectural facing; this small weathered specimen has little commercial value.
Geological facts
The contrasting dark inclusion is useful evidence of magma mixing or incorporation of surrounding rock. A steel knife should not easily scratch fresh quartz-rich grains, while feldspar may show cleavage faces.
Field identification & locations
Common worldwide in continental mountain belts and exposed shields; identify it by visible interlocking quartz/feldspar grains and the strong light–dark contrast. Estimated value: $1–$10 as a common hand specimen, or $10–$30 if locally collectible.
