igneous
Granite Cobble
Granite
Hardness (Mohs scale): 6 to 7. Color: White, gray, pink, and black salt-and-pepper appearance. Luster: Vitreous to dull (weathered). Crystal structure: Phaneritic (medium-to-coarse grained crystals). Cleavage: Varies by mineral (feldspar has 2 directions). Specific gravity: 2.63 to 2.75.
- Color
- White, gray, pink, and black salt-and-pepper appearance
- Luster
- Vitreous to dull (weathered)
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Physical properties
Hardness (Mohs scale): 6 to 7. Color: White, gray, pink, and black salt-and-pepper appearance. Luster: Vitreous to dull (weathered). Crystal structure: Phaneritic (medium-to-coarse grained crystals). Cleavage: Varies by mineral (feldspar has 2 directions). Specific gravity: 2.63 to 2.75.
Formation & geological history
Formed through the slow crystallization of magma below the Earth's surface (intrusive). This specimen has been rounded and smoothed by water or glacial transport, likely during the Holocene epoch or earlier.
Uses & applications
Crushed stone for construction, architectural veneer, decorative landscaping, and occasionally polished for paperweights or small decorative items.
Geological facts
Granite makes up a large part of the Earth's continental crust. It is primarily composed of quartz, feldspar, and mica. The black specks seen here are likely biotite mica or hornblende.
Field identification & locations
Identify by its interlocking granular texture and visible crystals of white/pink feldspar and clear quartz. Commonly found in riverbeds, glacial moraines, and mountains. For collectors, rounded river rocks like this are great for stone painting or lapidary tumbling.
