igneous
Granite
Granite (Felsic Plutonic Rock / SiO2 + Al2O3 + K2O + Na2O + CaO + FeO + MgO)
Hardness: 6-7 on Mohs scale. Color: Grayish-white with dark flecks. Luster: Vitreous to dull. Crystal structure: Phaneritic (medium-to-coarse grained) holocrystalline. Cleavage: Indistinct. Specific gravity: 2.63 to 2.75.
- Hardness
- 6-7 on Mohs scale
- Color
- Grayish-white with dark flecks
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Grayish-white with dark flecks. Luster: Vitreous to dull. Crystal structure: Phaneritic (medium-to-coarse grained) holocrystalline. Cleavage: Indistinct. Specific gravity: 2.63 to 2.75.
Formation & geological history
Formed from the slow cooling of silica-rich magma deep underground (plutonic). Found in continental crust across all geological ages, notably in Orogenic belts. Most specimens are hundreds of millions to billions of years old.
Uses & applications
Extensively used in construction for countertops, floor tiles, paving stones, and curbs. Crushed granite is used as aggregate in road building and concrete. Also used for monuments and cemeteries.
Geological facts
Granite is the most common igneous rock found on Earth's continents. It contains radioactive elements like thorium and uranium, which can decay into radon gas. Mount Rushmore is carved into a massive granite batholith in the Black Hills.
Field identification & locations
Identify in the field by its speckled 'salt and pepper' appearance and visible interlocking mineral crystals (quartz, feldspar, and biotite mica). Found worldwide in mountain ranges. Collectors look for unique color variants like 'pink granite' or large 'pegmatite' crystals.
