igneous
Rounded granite or granodiorite cobble
Granite–granodiorite, composed mainly of quartz, feldspar, and dark mica/amphibole
AI-generated identification · may be incorrectHardness about 6–7 Mohs; gray, tan, and black speckled color with a granular, crystalline texture and dull-to-subvitreous luster. No obvious cleavage as a whole rock; individual feldspar crystals may show cleavage. Specific gravity typically 2.6–2.8.
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Physical properties
Hardness about 6–7 Mohs; gray, tan, and black speckled color with a granular, crystalline texture and dull-to-subvitreous luster. No obvious cleavage as a whole rock; individual feldspar crystals may show cleavage. Specific gravity typically 2.6–2.8.
Formation & geological history
A coarse-grained intrusive igneous rock formed by slow cooling of silica-rich magma deep underground, generally during Precambrian to younger continental crust formation. Its rounded shape indicates transport and abrasion in a river, beach, or glacial environment.
Uses & applications
Used for construction aggregate, paving, curbing, monuments, landscaping, and decorative stone; this rounded specimen has mainly educational or modest collecting value.
Geological facts
The visible interlocking grains are characteristic of phaneritic plutonic rock. The specimen may be granodiorite rather than granite if plagioclase dominates over alkali feldspar.
Field identification & locations
Identify it by its hard, dense, salt-and-pepper granular texture and inability to scratch easily with a steel nail; quartz should resist scratching by a knife. Common worldwide in continental mountain belts, river gravels, and glacial deposits.
