igneous
Granite Cobble
Granite (Phaneritic Igneous Rock)
Hardness: 6-7 (Mohs); Color: Tan, beige, and orange with black flecks; Luster: Vitreous to dull; Structure: Phaneritic (visible crystals); Cleavage: None (fractures irregularly); Specific gravity: 2.63-2.75
- Hardness
- 6-7 (Mohs)
- Color
- Tan, beige, and orange with black flecks
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 (Mohs); Color: Tan, beige, and orange with black flecks; Luster: Vitreous to dull; Structure: Phaneritic (visible crystals); Cleavage: None (fractures irregularly); Specific gravity: 2.63-2.75
Formation & geological history
Formed from the slow cooling and crystallization of felsic magma beneath the Earth's surface. This specific specimen has been polished into a rounded shape by river or beach water action over thousands of years.
Uses & applications
Granite is used extensively in construction, countertops, and floor tiles. Cobble-sized pieces like this are often used in landscaping or as decorative garden stones.
Geological facts
Granite is one of the most common rocks in the Earth's continental crust. It contains quartz, feldspar, and mica (the black flecks seen here are likely biotite or hornblende).
Field identification & locations
Identify in the field by its 'salt and pepper' appearance and hardness (cannot be scratched by a steel knife). Commonly found in mountainous regions or as displaced glacial erratics and river rocks.
