igneous
Weathered granitic rock, likely granodiorite
Granodiorite: quartz, plagioclase feldspar, potassium feldspar, and biotite/hornblende
AI-generated identification · may be incorrectCoarse, mottled gray-white texture with dark mafic minerals and rusty iron-oxide staining; likely Mohs hardness 6–7, vitreous to dull luster, interlocking crystalline structure, and no prominent cleavage as a whole rock. The rounded shape indicates abrasion or weathering.
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Physical properties
Coarse, mottled gray-white texture with dark mafic minerals and rusty iron-oxide staining; likely Mohs hardness 6–7, vitreous to dull luster, interlocking crystalline structure, and no prominent cleavage as a whole rock. The rounded shape indicates abrasion or weathering.
Formation & geological history
A plutonic igneous rock crystallized slowly from magma deep in the continental crust, typically during Precambrian to Phanerozoic mountain-building events; its exact age cannot be determined from the image.
Uses & applications
Used as crushed aggregate, road stone, dimension stone, paving, and occasionally decorative landscaping material. Ordinary rounded specimens have little jewelry value.
Geological facts
Granodiorite is compositionally intermediate between granite and diorite and commonly resembles granite in hand samples. Rust-colored patches usually reflect oxidation of iron-bearing minerals.
Field identification & locations
Identify it by visible interlocking white plagioclase, gray quartz, pale feldspar, and black biotite or hornblende; it should scratch glass but not be scratched by a steel knife. Common in continental mountain belts and glacial or stream gravels.
