igneous
Granite
Phaneritic Intrusive Igneous Rock (composed of Quartz, Feldspar, and Mica)
Hardness: 6-7 Mohs; Color: Gray, pink, white, with black specks; Luster: Dull to pearly (vitreous on mineral faces); Crystal Structure: Phaneritic (coarse-grained); Cleavage: None (rock breaks unevenly); Specific Gravity: 2.63 - 2.75
- Hardness
- 6-7 Mohs
- Color
- Gray, pink, white, with black specks
- Luster
- Dull to pearly (vitreous on mineral faces)
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Physical properties
Hardness: 6-7 Mohs; Color: Gray, pink, white, with black specks; Luster: Dull to pearly (vitreous on mineral faces); Crystal Structure: Phaneritic (coarse-grained); Cleavage: None (rock breaks unevenly); Specific Gravity: 2.63 - 2.75
Formation & geological history
Formed from the slow cooling of silica-rich magma deep underground. This slow cooling allows for large, visible crystals to form. It can date back to any geological age where continental crust was forming, notably during the Precambrian and Paleozoic eras.
Uses & applications
Extensively used in construction for countertops, floor tiles, paving stones, and monuments due to its durability and aesthetic appeal. Also used as crushed stone in roadbeds and concrete.
Geological facts
Granite makes up the majority of Earth's continental crust. Mount Rushmore is carved into a massive granite batholith in South Dakota, and the rock's density makes it resistant to weathering over thousands of years.
Field identification & locations
Identify in the field by its 'salt and pepper' appearance and visible interlocking crystals. It is commonly found in mountain ranges (batholiths) and shields. For collectors, look for samples with larger crystals or unusual coloration from high orthoclase feldspar content.
