igneous
Granite
Granitoid (KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8 + SiO2)
Hardness: 6-7 Mohs; Color: Mottled pink, white, gray, and black; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained visible crystals); Cleavage: Poor; Specific Gravity: 2.63 to 2.75
- Hardness
- 6-7 Mohs
- Color
- Mottled pink, white, gray, and black
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 Mohs; Color: Mottled pink, white, gray, and black; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained visible crystals); Cleavage: Poor; Specific Gravity: 2.63 to 2.75
Formation & geological history
Formed by the slow crystallization of silica-rich magma beneath the Earth's surface (intrusive). They can be found in continental crust dating back billions of years to the Precambrian era.
Uses & applications
Extensively used in construction for countertops, floor tiles, paving stone, curbing, and monuments. Also used as crushed stone for road base and railroad ballast.
Geological facts
Granite is the most common igneous rock found on Earth's continental surface. The famous peaks of Yosemite National Park (like Half Dome) and Mount Rushmore are made entirely of granite.
Field identification & locations
Identify in the field by the 'salt and pepper' appearance of interlocking crystals of quartz (clear/gray), feldspar (pink/white), and mica (black). Commonly found in mountain ranges or Shield areas. Collectors look for unique inclusions or rare pegmatite formations.
