igneous
Granite
Plutonic Igneous Rock (composed primarily of Quartz, Feldspar, and Mica)
Hardness: 6-7 on Mohs scale; Color: Mottled gray, white, and tan; Luster: Vitreous to dull; Crystal Structure: Phaneritic (coarse-grained) crystalline; Cleavage: None (fractures irregularly); Specific Gravity: 2.63-2.75
- Hardness
- 6-7 on Mohs scale
- Color
- Mottled gray, white, and tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Mottled gray, white, and tan; Luster: Vitreous to dull; Crystal Structure: Phaneritic (coarse-grained) crystalline; Cleavage: None (fractures irregularly); 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, these intrusive rocks cool over thousands of years to create large visible crystals. Found throughout Earth's crust across all geological ages.
Uses & applications
Extensively used in construction for countertops, floor tiles, paving stones, and memorial monuments. Industrial uses include use as an aggregate in concrete and railroad ballast.
Geological facts
Granite makes up a large part of the continental crust. Half Dome in Yosemite National Park is one of the world's most famous granite monoliths. It is one of the hardest and most durable rocks common on the surface.
Field identification & locations
Identify by its 'salt and pepper' appearance and visible interlocking crystals. It is ubiquitous in mountainous regions and areas with exposed bedrock. Collectors look for unique mineral inclusions like tourmaline or garnets.
