igneous
Weathered granitic boulder
Granite to granodiorite; quartz–feldspar–biotite rock
AI-generated identification · may be incorrectCoarse-grained, gray to dark gray, with pale weathered feldspar and darker biotite/amphibole; typically Mohs 6–7, vitreous to dull luster, interlocking crystals, and no cleavage as a whole. The surface shows strong chemical weathering and possible iron staining.
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Physical properties
Coarse-grained, gray to dark gray, with pale weathered feldspar and darker biotite/amphibole; typically Mohs 6–7, vitreous to dull luster, interlocking crystals, and no cleavage as a whole. The surface shows strong chemical weathering and possible iron staining.
Formation & geological history
Formed by slow cooling of silica-rich magma deep in the crust, commonly during Precambrian to Paleozoic continental crust formation; later exposed and rounded by weathering, glacial transport, or stream action. Exact age and locality cannot be determined from the image.
Uses & applications
Commonly used for dimension stone, curbing, riprap, landscaping, monuments, countertops, and aggregate. This large weathered boulder has primarily landscaping value.
Geological facts
The rounded form and rind-like weathering may indicate a glacial erratic or spheroidally weathered outcrop fragment. Dark patches could be biotite-rich minerals, mafic inclusions, or surface staining.
Field identification & locations
Identify by visible interlocking quartz and feldspar grains, hardness, and resistance to scratching by a steel nail; vinegar should not fizz. Common worldwide, especially in granitic terranes and glaciated regions; a fresh broken surface is needed for confident identification.
