igneous
Granite
Granite (composed primarily of Quartz, Alkali Feldspar, and Plagioclase)
Hardness: 6-7 on Mohs scale; Color: Grayish-white with salt-and-pepper appearance; Luster: Dull to vitreous; Crystal structure: Phaneritic (coarse-grained); Cleavage: None (fractures); Specific gravity: 2.63 to 2.75
- Hardness
- 6-7 on Mohs scale
- Color
- Grayish-white with salt-and-pepper appearance
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Grayish-white with salt-and-pepper appearance; Luster: Dull to vitreous; Crystal structure: Phaneritic (coarse-grained); Cleavage: None (fractures); Specific gravity: 2.63 to 2.75
Formation & geological history
Formed through the slow crystallization of magma below Earth's surface (intrusive). Most granites date from the Precambrian to the Cenozoic eras, found in continental crustal plates.
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 makes up a large portion 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 available.
Field identification & locations
Identify by its 'salt and pepper' look and visible interlocking crystals. Common in mountain ranges and glacial till. For collectors, look for specimens with large 'phenocrysts' or unique mineral inclusions.
