igneous
Granite
Phaneritic plutonic rock (SiO2 > 69%)
Hardness: 6-7 on Mohs scale; Color: Gray, salt-and-pepper, with reddish-brown oxidation; Luster: Dull to vitreous; Crystal structure: Phaneritic (medium-grained); Cleavage: Indistinct; Specific gravity: 2.63-2.75.
- Hardness
- 6-7 on Mohs scale
- Color
- Gray, salt-and-pepper, with reddish-brown oxidation
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Gray, salt-and-pepper, with reddish-brown oxidation; Luster: Dull to vitreous; Crystal structure: Phaneritic (medium-grained); Cleavage: Indistinct; Specific gravity: 2.63-2.75.
Formation & geological history
Formed by the slow crystallization of silica-rich magma beneath the Earth's surface. This specimen appears weathered and oxidized, representative of continental crust formations often millions of years old.
Uses & applications
Extensively used in construction for countertops, floor tiles, paving stones, and monuments due to its durability and aesthetic appeal.
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
Identify in the field by checking for a visible interlocking crystalline texture of quartz and feldspar and a high resistance to scratching. Common in mountainous regions or areas with exposed glacial till.
