igneous
Granite
Granite (phaneritic intrusive igneous rock consisting mainly of quartz, alkali feldspar, and plagioclase)
Hardness: 6-7 on Mohs scale. Color: Mottled grey, white, pink, or red with dark specks. Luster: Vitreous to dull. Crystal Structure: Phaneritic (visible coarse-grained crystals). Cleavage: Varies by mineral content (feldspar has two, quartz has none). Specific Gravity: 2.63 to 2.75.
- Hardness
- 6-7 on Mohs scale
- Color
- Mottled grey, white, pink, or red with dark specks
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Mottled grey, white, pink, or red with dark specks. Luster: Vitreous to dull. Crystal Structure: Phaneritic (visible coarse-grained crystals). Cleavage: Varies by mineral content (feldspar has two, quartz has none). Specific Gravity: 2.63 to 2.75.
Formation & geological history
Formed from the slow crystallization of silica-rich magma beneath the Earth's surface (plutonic). It is found primarily in the continental crust and can range in age from the Precambrian to the Cenozoic eras.
Uses & applications
Extensively used as a dimension stone for countertops, flooring, and monuments due to its durability. Also used as crushed stone (aggregate) for road construction and foundations.
Geological facts
Granite makes up the majority of the Earth's continental crust. Famous natural formations like Yosemite's Half Dome and Mount Rushmore are composed of granite. It is one of the hardest and most common rocks on the planet.
Field identification & locations
Identify in the field by its 'salt and pepper' appearance and visible interlocking crystals of different colors. It is found in mountain ranges and continental shields. Collectors look for large crystals or unusual mineral inclusions.
