igneous
Granite
Phaneritic Intrusive Igneous Rock (primarily composed of SiO2, Al2O3, K2O, Na2O)
Hardness: 6-7 on Mohs scale; Color: Salt-and-pepper (white, grey, and black); Luster: Dull to Vitreous; Crystal Structure: Phaneritic (coarse-grained, visible crystals); Cleavage: None (it fractures unevenly); Specific Gravity: 2.63 to 2.75
- Hardness
- 6-7 on Mohs scale
- Color
- Salt-and-pepper (white, grey, and black)
- Luster
- Dull to Vitreous
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Salt-and-pepper (white, grey, and black); Luster: Dull to Vitreous; Crystal Structure: Phaneritic (coarse-grained, visible crystals); Cleavage: None (it fractures unevenly); Specific Gravity: 2.63 to 2.75
Formation & geological history
Formed from the slow crystallization of magma below Earth's surface (plutonic). It is found in large masses known as batholiths which form the core of many mountain ranges. Most granite dates from the Precambrian to Cenozoic eras.
Uses & applications
Extensively used in construction for countertops, floor tiles, paving stones, curbing, and monuments. Due to its durability and aesthetic appeal, it is a primary material for architecture and interior design.
Geological facts
Granite makes up a large portion of the Earth's continental crust. Mount Rushmore is carved into a granite batholith. It often contains trace amounts of radioactive elements like uranium and thorium, which can lead to the emission of radon gas.
Field identification & locations
Identify in the field by its 'salt and pepper' look where individual crystals of quartz (clear/grey), feldspar (white/pink), and mica or hornblende (black) are large enough to see with the naked eye. Found globally in continental shields and mountain belts. Collectors look for large, well-defined accessory minerals or unique colorations.
