igneous
Granite
Phaneritic Felsic Igneous Rock (primarily Quartz, Feldspar, and Mica)
Hardness: 6-7 on Mohs scale; Color: typically mottled grey, white, pink, or tan with black specks; Luster: Vitreous to pearly; Crystal structure: Coarse-grained phaneritic texture; Cleavage: None (it fractures); Specific gravity: 2.63 - 2.75.
- Hardness
- 6-7 on Mohs scale
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-7 on Mohs scale; Color: typically mottled grey, white, pink, or tan with black specks; Luster: Vitreous to pearly; Crystal structure: Coarse-grained phaneritic texture; Cleavage: None (it fractures); Specific gravity: 2.63 - 2.75.
Formation & geological history
Formed from the slow crystallization of silica-rich magma deep underground (plutonic). It can form during any geological era but is a primary component of continental crust. It takes millions of years to cool, allowing for visible crystals.
Uses & applications
Extensively used as dimension stone in construction for countertops, floor tiles, and monuments. Also used in crushed form for road base and railroad ballast. Highly valued as a durable decorative stone.
Geological facts
Granite makes up a large part of the Earth's continental crust. Mount Rushmore is carved into a granite batholith. It is one of the hardest and most durable natural stones, which is why it has been used in architecture since Ancient Egypt.
Field identification & locations
Identify in the field by its 'salt and pepper' appearance and large, interlocked visible crystals. It is found in mountain ranges and Shields (like the Canadian Shield). Look for lack of layering and a very hard surface that cannot be scratched by a steel knife.
