igneous
Granite River Cobble
Phaneritic Felsic Igneous Rock
Hardness: 6-7 Mohs; Color: Pink, grey, and white with black specks; Luster: Dull/Matte (weathered); Crystal structure: Phaneritic (visible crystals); Cleavage: None (fractures); Specific gravity: 2.6-2.7
- Hardness
- 6-7 Mohs
- Color
- Pink, grey, and white with black specks
- Luster
- Dull/Matte (weathered)
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Physical properties
Hardness: 6-7 Mohs; Color: Pink, grey, and white with black specks; Luster: Dull/Matte (weathered); Crystal structure: Phaneritic (visible crystals); Cleavage: None (fractures); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the slow cooling of silica-rich magma deep underground, often millions of years ago. This specific specimen has been smoothed and rounded by water transport in a river or glacial environment.
Uses & applications
Commonly used as decorative landscaping stone, in construction aggregates, and when large/pure enough, for countertops and monuments.
Geological facts
Granite makes up a large portion of the Earth's continental crust. The pink color in this specimen is caused by potassium feldspar (orthoclase).
Field identification & locations
Identify by its 'salt and pepper' appearance and visible interlocking crystals of quartz, feldspar, and mica. Commonly found in glacial till and riverbeds across North America.
