igneous
Likely weathered brown quartz-bearing rock
Tentatively weathered granite or granitic gneiss; exact identification is uncertain from the photograph
AI-generated identification · may be incorrectBrown to dark gray, coarse and irregular, with a dull earthy to locally granular luster. Likely contains quartz, feldspar, and dark mica; hardness approximately 6–7, with little visible cleavage and variable specific gravity around 2.6–2.8.
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Physical properties
Brown to dark gray, coarse and irregular, with a dull earthy to locally granular luster. Likely contains quartz, feldspar, and dark mica; hardness approximately 6–7, with little visible cleavage and variable specific gravity around 2.6–2.8.
Formation & geological history
Probably formed by slow cooling of silica-rich magma deep underground, possibly later metamorphosed and strongly weathered; such rocks are commonly Precambrian to Paleozoic in age depending on locality.
Uses & applications
Used as crushed aggregate, building stone, and landscape rock; attractive polished pieces may be used decoratively. This rough fragment has minimal commercial value.
Geological facts
The rusty-brown color commonly results from oxidation of iron-bearing minerals such as biotite or amphibole. A glassy quartz grain should scratch ordinary glass, while feldspar grains are typically blocky and opaque.
Field identification & locations
Common in continental crust and found worldwide, especially in mountain belts and exposed shield regions. A hand lens, fresh broken surface, streak test, and acid test help distinguish granite from altered volcanic or metamorphic rocks.
