igneous
Granite
Plutonic Igneous Rock (composed of Quartz, Feldspar, and Mica)
Hardness: 6-7 on Mohs scale. Color: Mottled buff, pink, white, and gray with dark specks. Luster: Vitreous to dull. Structure: Phaneritic (coarse-grained) crystalline. Cleavage: Indistinct in bulk, but feldspar grains show two planes at 90 degrees.
- Hardness
- 6-7 on Mohs scale
- Color
- Mottled buff, pink, white, and gray with dark specks
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Mottled buff, pink, white, and gray with dark specks. Luster: Vitreous to dull. Structure: Phaneritic (coarse-grained) crystalline. Cleavage: Indistinct in bulk, but feldspar grains show two planes at 90 degrees.
Formation & geological history
Formed from the slow crystallization of magma below Earth's surface (intrusive). Geological age varies from Archean to Cenozoic depending on the specific batholith; common in continental crust platforms.
Uses & applications
Extensively used in construction for countertops, floor tiles, paving stones, and memorial monuments. Also used as crushed stone (aggregate) for road base and concrete.
Geological facts
Granite makes up the majority of the Earth's continental crust. Mount Rushmore is carved into a massive granite batholith in South Dakota. Because it contains trace amounts of uranium, some granite can emit small amounts of radon gas.
Field identification & locations
Identify in the field by its 'salt and pepper' appearance and visible interlocking crystals of quartz (translucent) and feldspar (opaque/pink/white). Common in mountainous regions and shield areas. It is very resistant to weathering.
