igneous
Granite
Granite (Phaneritic intrusive igneous rock) - Composition: SiO2, Al2O3, K2O, Na2O
Hardness: 6-7 on Mohs scale; Color: Pink, white, gray, and black speckles; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained visible crystals); Cleavage: Distinct in feldspar minerals, none in quartz; Specific gravity: 2.63 to 2.75
- Hardness
- 6-7 on Mohs scale
- Color
- Pink, white, gray, and black speckles
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Pink, white, gray, and black speckles; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained visible crystals); Cleavage: Distinct in feldspar minerals, none in quartz; Specific gravity: 2.63 to 2.75
Formation & geological history
Formed through the slow crystallization of magma below Earth's surface (plutonic). Found in continental crust, often dating from the Precambrian to Cenozoic eras, typically in mountain belts or cratons.
Uses & applications
Extensively used in construction for countertops, floor tiles, curbing, and gravestones. Also used as crushed stone (aggregate) for road base and railroad ballast.
Geological facts
Granite makes up the core of most continents. It is one of the hardest natural stones, which is why it's a preferred material for monuments that are meant to last centuries. Mount Rushmore is carved into a granite batholith.
Field identification & locations
Identify in the field by its 'salt and pepper' look with visible mineral grains of quartz (translucent), feldspar (opaque white/pink), and mica (shiny black flakes). Common in mountainous regions like the Sierra Nevada or Appalachians.
