igneous
Weathered granite or granodiorite
Coarse-grained intrusive felsic igneous rock; chiefly quartz, plagioclase feldspar, potassium feldspar, and dark biotite/hornblende
AI-generated identification · may be incorrectTypically Mohs 6–7, pale gray to tan, with a granular crystalline texture and dull to slight glassy luster on fresh grains; massive, with no obvious cleavage as a whole. The specimen appears weathered and may contain iron-oxide staining and small mafic minerals.
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Physical properties
Typically Mohs 6–7, pale gray to tan, with a granular crystalline texture and dull to slight glassy luster on fresh grains; massive, with no obvious cleavage as a whole. The specimen appears weathered and may contain iron-oxide staining and small mafic minerals.
Formation & geological history
Formed when silica-rich magma cooled slowly deep underground, producing visible interlocking crystals; its exact age cannot be determined from the image and may range from Precambrian to Cenozoic depending on locality.
Uses & applications
Widely used as dimension stone, paving, curbing, monuments, countertops, aggregate, and crushed stone; ordinary pieces have little jewelry value.
Geological facts
Granite is defined by abundant quartz and alkali feldspar, whereas granodiorite contains more plagioclase; distinguishing them visually often requires a thin section or modal mineral analysis.
Field identification & locations
Look for visible quartz grains, abundant pale feldspar, and scattered black biotite or hornblende; a streak test is usually white, and acid produces no significant reaction. Common worldwide in continental plutons and exposed mountain ranges.
