igneous
Granite
Phaneritic Plutonic Felsic Rock (KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8 + SiO2)
Hardness: 6-7 on Mohs scale; Color: Pink, white, gray, and black speckles; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Cleavage: No overall cleavage (individual minerals like mica may have it); Specific gravity: 2.63 - 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); Cleavage: No overall cleavage (individual minerals like mica may have it); Specific gravity: 2.63 - 2.75
Formation & geological history
Formed from the slow underground crystallization of magma (plutonic). Found in continental crust within mountain belts and shields. Geological age ranges from over 3.8 billion years to recently formed intrusion zones.
Uses & applications
Extensively used in construction for countertops, floor tiles, paving stones, monuments, and as crushed stone for road base and concrete aggregate.
Geological facts
Granite is the most common igneous rock found at the Earth's surface. Mount Rushmore and the Egyptian pyramids contain significant amounts of granite or syenite. It often contains radioactive elements like uranium, though usually in harmless amounts.
Field identification & locations
Identify by its interlocking 'salt and pepper' appearance of quartz (gray/clear), feldspar (pink/white), and biotite/hornblende (black). It is found globally in mountainous and cratonic regions. For collectors, it is best found in glacial till or at quarry sites.
