igneous
Weathered granite or granitic gneiss
Quartz–feldspar–mica aggregate; approximate granite composition
AI-generated identification · may be incorrectHardness about 6–7 Mohs; pale gray to tan, granular texture, dull to weakly sparkly luster, with visible quartz/feldspar and minor dark mica or iron staining. Crystals are interlocking and lack cleavage as a rock, though feldspar grains cleave.
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Physical properties
Hardness about 6–7 Mohs; pale gray to tan, granular texture, dull to weakly sparkly luster, with visible quartz/feldspar and minor dark mica or iron staining. Crystals are interlocking and lack cleavage as a rock, though feldspar grains cleave.
Formation & geological history
Formed by slow cooling of silica-rich magma deep in the crust, likely Precambrian to Paleozoic in age, then exposed and rounded by weathering and transport. The image may also represent a weakly foliated granitic gneiss, but foliation is not clear.
Uses & applications
Commonly used as crushed aggregate, building stone, monuments, countertops, and decorative landscaping rock; this small weathered piece has little commercial value.
Geological facts
Granite’s light color reflects abundant quartz and feldspar, while brown patches commonly result from oxidation of iron-bearing minerals or weathering of biotite.
Field identification & locations
Identify it by its coarse interlocking grains, quartz’s glassy appearance, feldspar’s blocky white grains, and occasional mica flakes; it commonly occurs in continental shields, mountain belts, and glacial or stream gravels.
