igneous
Grey Granite
Phaneritic Felsic Igneous Rock (primarily Quartz, Feldspar, and Mica)
Hardness: 6-7 (Mohs scale); Color: Salt-and-pepper grey, white, and black mottled; Luster: Dull to vitreous; Crystal Structure: Phaneritic (visible interlocking crystals); Cleavage: Indistinct in bulk, but feldspar grains show cleavage; Specific Gravity: 2.63 - 2.75
- Hardness
- 6-7 (Mohs scale)
- Color
- Salt-and-pepper grey, white, and black mottled
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Salt-and-pepper grey, white, and black mottled; Luster: Dull to vitreous; Crystal Structure: Phaneritic (visible interlocking crystals); Cleavage: Indistinct in bulk, but feldspar grains show cleavage; Specific Gravity: 2.63 - 2.75
Formation & geological history
Formed through the slow crystallization of magma below the Earth's surface (intrusive). Granite can date from the Archean Eon to the Cenozoic, typically found in continental crust and mountain ranges.
Uses & applications
Extensively used in construction for countertops, floor tiles, paving stones, and monuments. Also used as crushed stone (aggregate) for road base and concrete.
Geological facts
Granite is the most common rock found in the Earth's continental crust. El Capitan in Yosemite National Park is one of the world's most famous granite monoliths.
Field identification & locations
Identify in the field by its coarse-grained, 'salt and pepper' appearance and extreme hardness (will readily scratch glass). Found in batholiths and mountain cores globally, such as the Appalachians or the Scottish Highlands.
