igneous
Granite
Granite (composed primarily of Quartz SiO2, Alkali Feldspar (K,Na)AlSi3O8, and Plagioclase Feldspar)
Hardness: 6-7 on Mohs scale; Color: Mottled pink, gray, white, and black; Luster: Vitreous to dull; Structure: Phaneritic (coarse-grained) crystalline; Cleavage: None (though feldspars within show cleavage); Specific Gravity: 2.63 to 2.75
- Hardness
- 6-7 on Mohs scale
- Color
- Mottled pink, gray, white, and black
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Mottled pink, gray, white, and black; Luster: Vitreous to dull; Structure: Phaneritic (coarse-grained) crystalline; Cleavage: None (though feldspars within show cleavage); Specific Gravity: 2.63 to 2.75
Formation & geological history
Formed through the slow crystallization of silica-rich magma beneath the Earth's surface (intrusive). The large visible crystals indicate a long cooling process. Ages range from Archean to recent, depending on the specific pluton.
Uses & applications
Extensively used in construction for countertops, floor tiles, and paving stones. Also used in monuments, curbing, and as aggregate for roads. Occasional use in jewelry as polished 'granite jasper' or tumbled stones.
Geological facts
Granite makes up a large portion of the Earth's continental crust. Famous landmarks like Mount Rushmore and Yosemite's El Capitan are carved into or composed of granite. It is extremely durable and resistant to acid rain.
Field identification & locations
Identify by its 'salt and pepper' look with visible, interlocking crystals of different colors. It will not be scratched by a steel knife. Commonly found in mountainous regions or areas where ancient crust is exposed (shields). Look for the mix of translucent quartz and opaque pink or white feldspar.
