igneous
Granite Cobble
Granite (Felsic Intrusive)
Hardness: 6-7 on Mohs scale. Color: Mottled salt-and-pepper (white, gray, pink, black). Luster: Dull to vitreous. Structure: Phaneritic (coarse-grained crystals). Specific Gravity: 2.63 - 2.75.
- Hardness
- 6-7 on Mohs scale
- Color
- Mottled salt-and-pepper (white, gray, pink, black)
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Mottled salt-and-pepper (white, gray, pink, black). Luster: Dull to vitreous. Structure: Phaneritic (coarse-grained crystals). Specific Gravity: 2.63 - 2.75.
Formation & geological history
Formed from the slow subterranean cooling of silica-rich magma (plutonic). This specific specimen is a water-worn river cobble, rounded by abrasive action over thousands of years.
Uses & applications
Commonly used in large scale construction, kitchen countertops, paving stones, and as crushed decorative gravel.
Geological facts
Granite makes up a large portion of the Earth's continental crust. Mount Rushmore is carved into a massive granite batholith in the Black Hills of South Dakota.
Field identification & locations
Identifiable by its granular texture and visible interlocking crystals of quartz, feldspar, and mica. It is found globally in mountainous regions and glacial deposits. For collectors, it represents a classic intrusive igneous rock.
