Granite

Physical Properties

Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' (gray, white, and black); Luster: Vitreous to pearly; Crystal structure: Phaneritic (coarse-grained visible crystals); Cleavage: Indistinct; Specific gravity: 2.63 to 2.75.

Formation & Geological History

Formed from the slow cooling and crystallization of magma deep beneath the Earth's surface (plutonic). It is primarily composed of quartz, feldspar, and mica. Geological ages vary from Precambrian to Cenozoic.

Uses & Applications

Extensively used in construction for countertops, floor tiles, paving stones, curbing, and monuments. Due to its durability and aesthetics, it is also a choice for architectural facades and decorative gravel.

Geological Facts

Granite makes up a large portion of the Earth's continental crust. Mount Rushmore is carved into a granite batholith, and the rock is famous for its extreme resistance to acid rain and physical weathering.

Field Identification & Locations

Identify in the field by its speckled, interlocking crystalline texture where crystals are visible to the naked eye. Look for the glint of mica flakes and the hardness that prevents it from being scratched by a steel knife. Common in mountain ranges and continental shields.

Identified on: 4/20/2026

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