igneous
Granite fragment
Granite (Felsic intrusive igneous rock)
Hardness: 6-7 Mohs; Color: Pinkish-grey, white, and black mottled appearance; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Cleavage: Distinct in feldspar components; Specific gravity: 2.63 to 2.75.
- Hardness
- 6-7 Mohs
- Color
- Pinkish-grey, white, and black mottled appearance
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 Mohs; Color: Pinkish-grey, white, and black mottled appearance; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Cleavage: Distinct in feldspar components; Specific gravity: 2.63 to 2.75.
Formation & geological history
Formed from the slow crystallization of magma below Earth's surface. Primarily composed of quartz, feldspar, and mica. Geological age can range from Precambrian to Cenozoic depending on the specific location.
Uses & applications
Used extensively in construction (countertops, flooring), monument carving, and as crushed stone for road base and railroad ballast.
Geological facts
Granite makes up a large portion of the Earth's continental crust. Mount Rushmore is carved into a massive granite batholith in South Dakota.
Field identification & locations
Identified by its visible interlocking crystals of different colors. It is one of the most common rocks found in continental mountain ranges. For collectors, look for high variations in mineral sizing or unusual accessory minerals.
