igneous
Granite
Granite (composed primarily of Quartz SiO2, Alkali Feldspar KAlSi3O8, and Plagioclase)
Hardness: 6-7 Mohs; Color: Pinkish-grey with black speckles (biotite/hornblende); Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained visible crystals); Cleavage: None in the rock itself, though mineral components may show it; Specific gravity: 2.63 to 2.75.
- Hardness
- 6-7 Mohs
- Color
- Pinkish-grey with black speckles (biotite/hornblende)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 Mohs; Color: Pinkish-grey with black speckles (biotite/hornblende); Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained visible crystals); Cleavage: None in the rock itself, though mineral components may show it; Specific gravity: 2.63 to 2.75.
Formation & geological history
Formed through the slow crystallization of magma below Earth's surface (intrusive). Geological age varies from Precambrian to Cenozoic. It forms the core of many mountain ranges and continental crust.
Uses & applications
Major use in construction (countertops, floor tiles, paving stones), dimension stone for monuments and curbing, and crushed stone for road base or railroad ballast.
Geological facts
Mount Rushmore is carved into a massive granite batholith in South Dakota. Granite is one of the hardest and most durable common stones, which is why it has been used for thousands of years in architecture, including Ancient Egyptian pyramids.
Field identification & locations
Identify in the field by its 'salt and pepper' appearance and visible, interlocking crystals of quartz, feldspar, and dark mica. It is found globally in continental shields. Collectors look for unique mineral inclusions like tourmaline or large feldspar phenocrysts.
