igneous
Granite
Phaneritic plutonic igneous rock (Alkali-feldspar granite)
Hardness: 6-7 Mohs; Color: Mottled pink, grey, and black; Luster: Dull to vitreous; Crystal Structure: Phaneritic (coarse-grained); Cleavage: Distinct in feldspar grains; Specific Gravity: 2.63-2.75
- Hardness
- 6-7 Mohs
- Color
- Mottled pink, grey, and black
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 Mohs; Color: Mottled pink, grey, and black; Luster: Dull to vitreous; Crystal Structure: Phaneritic (coarse-grained); Cleavage: Distinct in feldspar grains; Specific Gravity: 2.63-2.75
Formation & geological history
Formed from the slow crystallization of magma below Earth's surface. High in silica and alkali metals, typically found in continental crust; ages range from billions of years to relatively young mountain roots.
Uses & applications
Extensively used in construction for countertops, floor tiles, paving stones, curbing, and monuments. Also used by gem collectors when polished.
Geological facts
Granite is the most common rock in Earth's continental crust. Mount Rushmore is carved into a granite batholith. Historically, it was used for the pyramids of Egypt and Stonehenge's inner circle.
Field identification & locations
Identify by its salt-and-pepper appearance and visible crystals of quartz, feldspar, and mica. It is most commonly found in mountainous regions or as glacial erratic stones in riverbeds.
