igneous
Granite
Phaneritic plutonic rock (composed of Quartz, Feldspar, and Mica/Amphibole)
Hardness: 6-7 on Mohs scale; Color: Salt-and-pepper (mottled grey, white, and black); Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained visible crystals); Cleavage: Dependent on mineral (feldspar has two planes, quartz has none); Specific gravity: 2.63 - 2.75
- Hardness
- 6-7 on Mohs scale
- Color
- Salt-and-pepper (mottled grey, white, and black)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Salt-and-pepper (mottled grey, white, and black); Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained visible crystals); Cleavage: Dependent on mineral (feldspar has two planes, quartz has none); Specific gravity: 2.63 - 2.75
Formation & geological history
Formed from the slow cooling and solidification of silica-rich magma deep underground (plutonic). Found in continental crust, often dating back to various orogenic (mountain-building) events across geological time.
Uses & applications
Extensively used in construction as dimension stone, countertops, floor tiles, and as crushed stone for road base or railway ballast. Its durability and aesthetic appeal also make it popular for monuments and sculptures.
Geological facts
Granite makes up a large portion of the Earth's continental crust and is unique to Earth among the planets in our solar system. The famous peaks in Yosemite National Park and the faces on Mount Rushmore are carved from granite.
Field identification & locations
Identify in the field by its interlocking, visible 'speckled' crystals that are uniform throughout the rock rather than in layers. It is ubiquitous in mountainous regions and shield areas like the Canadian Shield or the Appalachians. Collectors look for 'pegmatites' where the crystal sizes are exceptionally large.
