Igneous
Granite
Granite (composed primarily of Quartz SiO2, Orthoclase KAlSi3O8, and Plagioclase NaAlSi3O8 to CaAl2Si2O8)
Hardness: 6-7 on Mohs scale; Color: Pink, white, and grey mottled; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained) crystalline; Cleavage: None (though constituent minerals like feldspar have cleavage); Specific gravity: 2.63 to 2.75.
- Hardness
- 6-7 on Mohs scale
- Color
- Pink, white, and grey mottled
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Pink, white, and grey mottled; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained) crystalline; Cleavage: None (though constituent minerals like feldspar have cleavage); Specific gravity: 2.63 to 2.75.
Formation & geological history
Formed by the slow crystallization of magma below Earth's surface (intrusive). The pink hue indicates a high concentration of potassium feldspar. It can range in age from billions of years (Precambrian) to more recent tectonic events.
Uses & applications
Extensively used in construction for countertops, floor tiles, paving stones, curbing, and monuments. Also used 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. It is one of the hardest and most durable natural stones available.
Field identification & locations
Identify in the field by its 'salt and pepper' or interlocking crystalline appearance where individual mineral grains (quartz, feldspar, mica) are visible to the naked eye. Found globally in mountainous regions and continental shields. Collectors value unique veining or large crystal inclusions.
