igneous
Coarse-grained gray igneous rock, likely granite or granodiorite
Granite–granodiorite; chiefly quartz, feldspar, and dark mica/amphibole
AI-generated identification · may be incorrectHardness about 6–7 Mohs; mottled gray, white, and dark grains with a granular texture and generally dull to glassy luster. Interlocking crystals and no obvious layering or cleavage are typical; density is approximately 2.6–2.8 g/cm³.
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Physical properties
Hardness about 6–7 Mohs; mottled gray, white, and dark grains with a granular texture and generally dull to glassy luster. Interlocking crystals and no obvious layering or cleavage are typical; density is approximately 2.6–2.8 g/cm³.
Formation & geological history
Forms when silica-rich magma cools slowly beneath the surface, allowing visible crystals to grow. Individual pieces may range from Precambrian to Cenozoic in age depending on locality.
Uses & applications
Widely used as crushed stone, aggregate, building stone, countertops, monuments, and paving; ordinary hand specimens have little commercial value.
Geological facts
The dark minerals are likely biotite mica or hornblende, while pale grains are feldspar and possible quartz. A hand lens and dilute acid test can help distinguish it from carbonate rocks; it should not fizz.
Field identification & locations
Common in continental mountain belts and exposed plutons worldwide, including the Sierra Nevada, Canadian Shield, Appalachians, and Scandinavia. Confirm with a fresh broken surface, visible quartz, and hardness greater than a steel knife.
