Granite

Physical Properties

Hardness: 6-7 (Mohs scale); Color: Mottle gray, white, and black; Luster: Phaneritic (crystalline), vitreous (glassy) in quartz grains; Crystal Structure: Coarse-grained phaneritic; Cleavage: Dependent on mineral (felspar has 2 planes); Specific Gravity: 2.63 - 2.75

Formation & Geological History

Formed from the slow crystallization of magma below Earth's surface (intrusive). Commonly found in continental crust and batholiths; ages range from billions of years (Precambrian) to relatively recent eras.

Uses & Applications

Extensively used in construction for countertops, floor tiles, paving stone, and curbing. It is also used as dimension stone in monuments and as crushed aggregate for infrastructure.

Geological Facts

Granite makes up a large portion of the Earth's continental crust. Because it contains radioactive elements like uranium, it can naturally emit small amounts of radon gas.

Field Identification & Locations

Identify by its 'salt and pepper' appearance and visible interlocking crystals of quartz, feldspar, and mica. It will scratch glass and does not react with acid. Commonly found in mountainous regions or areas with glacial till.

Identified on: 4/18/2026

Mode: Standard