igneous
Granite
Phaneritic Igneous Rock (composed primarily of Quartz, Alkali Feldspar, and Plagioclase)
Hardness: 6-7 on Mohs scale; Color: typically white, pink, or gray with dark specks; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Cleavage: None (though feldspar components have cleavage); Specific Gravity: 2.63 to 2.75
- Hardness
- 6-7 on Mohs scale
- Color
- typically white, pink, or gray with dark specks
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: typically white, pink, or gray with dark specks; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Cleavage: None (though feldspar components have cleavage); Specific Gravity: 2.63 to 2.75
Formation & geological history
Formed by the slow crystallization of magma below Earth's surface (intrusive). The process can take millions of years, and these rocks are found in continental crust across all geological ages, notably in mountain-building belts.
Uses & applications
Extensively used in construction for countertops, floor tiles, paving stones, curbing, and monuments. It is also crushed into aggregate for road base and concrete.
Geological facts
Granite makes up a large portion of the Earth's continental crust. Mount Rushmore is carved into a granite batholith, and some of the oldest known rocks on Earth are granitic gneisses dating back over 4 billion years.
Field identification & locations
Identify in the field by its 'salt and pepper' appearance and visible interlocking crystals. It is found globally in mountain ranges and shield areas. Collectors look for unique mineral inclusions like tourmaline or large feldspar phenocrysts.
