Igneous
Granite
Granite (composed primarily of Quartz SiO2, Potassium Feldspar KAlSi3O8, and Plagioclase)
Hardness: 6-7 on Mohs scale. Color: Mottled pink, white, and grey. Luster: Vitreous to pearly. Crystal structure: Phaneritic (coarse-grained visible crystals). Cleavage: Varies by mineral constituent; no overall cleavage. Specific gravity: 2.63 to 2.75.
- Hardness
- 6-7 on Mohs scale
- Color
- Mottled pink, white, and grey
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Mottled pink, white, and grey. Luster: Vitreous to pearly. Crystal structure: Phaneritic (coarse-grained visible crystals). Cleavage: Varies by mineral constituent; no overall cleavage. Specific gravity: 2.63 to 2.75.
Formation & geological history
Formed from the slow cooling and crystallization of silica-rich magma deep within the Earth's crust (plutonic). Found in continental crust ranging from the Archean Eon to the Cenozoic Era.
Uses & applications
Extensively used in construction for countertops, floor tiles, and paving stones. Also used in monuments, curbing, and as crushed stone for road base and railway ballast.
Geological facts
Granite makes up the majority of the Earth's continental crust. Mount Rushmore is carved into a massive granite batholith in South Dakota. Because of its hardness, it was used by ancient Egyptians for sarcophagi and obelisks.
Field identification & locations
Identify by its 'salt and pepper' appearance and visible interlocking crystals of different colors. Commonly found in mountain ranges (orogenic belts) and glacial deposits. Collectors look for unique vein patterns or large phenocrysts (porphyritic texture).
