igneous
Granite
Phaneritic intrusive igneous rock (composed mainly of Quartz SiO2, Feldspar KAlSi3O8, and Biotite/Mica)
Hardness: 6-7 Mohs; Color: Salt and pepper appearance with pink, white, and dark grey/black flecks; Luster: Vitreous to pearly; Crystal structure: Phaneritic (coarse-grained visible crystals); Cleavage: Perfect on feldspar grains, none on quartz.
- Hardness
- 6-7 Mohs
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-7 Mohs; Color: Salt and pepper appearance with pink, white, and dark grey/black flecks; Luster: Vitreous to pearly; Crystal structure: Phaneritic (coarse-grained visible crystals); Cleavage: Perfect on feldspar grains, none on quartz.
Formation & geological history
Formed from the slow crystallization of magma below Earth's surface. It is a plutonic rock that cools over thousands of years, allowing large crystals to grow. Most granite dates from the Precambrian to Cenozoic eras.
Uses & applications
Extensively used in construction for countertops, flooring, curbing, and monuments. It is also used as crushed stone for road base and railroad ballast due to its high durability and strength.
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. It is one of the hardest and most common rocks on the planet.
Field identification & locations
Identify by looking for intergrown visible crystals of quartz (glassy), feldspar (opaque white/pink), and mica (shiny black flakes). Found globally in mountain ranges and continental shields like the Canadian Shield or the Appalachians.
