igneous
Polished dark speckled stone, likely granite or diorite
Granite–diorite granitoid; chiefly quartz, feldspar, and dark mafic minerals
AI-generated identification · may be incorrectGray-black, rounded and highly polished, with visible interlocking grains and no obvious layering. Typical hardness is about 6–7 Mohs; vitreous to dull luster, granular crystalline texture, and no cleavage as a whole rock.
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Physical properties
Gray-black, rounded and highly polished, with visible interlocking grains and no obvious layering. Typical hardness is about 6–7 Mohs; vitreous to dull luster, granular crystalline texture, and no cleavage as a whole rock.
Formation & geological history
An intrusive igneous rock formed when silica-rich magma cooled slowly deep underground, producing coarse crystals; its exact geological age cannot be determined from the image. The specimen appears tumbled or cabochon-polished.
Uses & applications
Used as a decorative stone, countertops, monuments, aggregate, and ornamental cabochons. This small piece has modest value unless it is a distinctive local or collectible variety.
Geological facts
The light grains are probably feldspar or quartz, while the black grains may be biotite, amphibole, or pyroxene. Diorite is generally darker and contains less quartz than granite, making visual identification alone uncertain.
Field identification & locations
Common worldwide, including India, Brazil, Scandinavia, Canada, and the United States. A hand lens, acid test, and mineral-grain identification can distinguish granite from diorite; typical value is $2–$15 for a small polished specimen.
