Igneous
Granite (including Pegmatite variants)
Phaneritic Plutonic Rock (composed primarily of Quartz SiO2, Feldspar KAlSi3O8, and Biotite/Muscovite mica)
Hardness: 6-7 on Mohs scale. Color: Mottled white, gray, black, and sometimes pink. Luster: Vitreous to pearly. Crystal structure: Phaneritic (visible crystals). Cleavage: Varies by mineral constituent. Specific gravity: 2.63 to 2.75.
- Hardness
- 6-7 on Mohs scale
- Color
- Mottled white, gray, black, and sometimes pink
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Mottled white, gray, black, and sometimes pink. Luster: Vitreous to pearly. Crystal structure: Phaneritic (visible crystals). Cleavage: Varies by mineral constituent. Specific gravity: 2.63 to 2.75.
Formation & geological history
Formed from the slow crystallization of magma below Earth's surface. These are deep-seated plutonic rocks often associated with continental crust formation, typically dating from the Precambrian to Cenozoic eras.
Uses & applications
Extensively used in construction (countertops, flooring, monuments), as crushed stone for road base, and as decorative landscaping or collector specimens when containing large crystals.
Geological facts
Granite is the most common rock found on Earth's continental crust. Because it cools extremely slowly underground, the individual mineral crystals have time to grow large enough to be seen with the naked eye.
Field identification & locations
Identify in the field by its 'salt and pepper' appearance and hardness (it will not be scratched by a steel knife). Common in mountain ranges and glacial deposits. Look for the distinct cleavage of mica flakes and the glassy look of quartz.
