Granite

Physical Properties

Hardness: 6-7 on Mohs scale; Color: Gray, salt-and-pepper, yellowish-tan with black specks; Luster: Dull to vitreous; Crystal structure: Phaneritic (coarse-grained crystals visible to the naked eye); Specific gravity: 2.63 - 2.75.

Formation & Geological History

Formed through the slow crystallization of magma below the Earth's surface (intrusive). The coarse grains indicate a slow cooling process over thousands of years. It can date from the Archean Eon to the Cenozoic Era.

Uses & Applications

Extensively used in construction for countertops, floor tiles, paving stones, curbing, and as monument stone or decorative gravel (crushed stone).

Geological Facts

Granite makes up a large portion of the Earth's continental crust. It is one of the hardest and most durable common stones, making it the preferred choice for monuments like Mount Rushmore.

Field Identification & Locations

Identify in the field by its interlocking mineral grains (quartz, feldspar, and mica). It will not be scratched by a steel knife. Common in mountain ranges and ancient shield areas like the Canadian Shield or the Appalachians.

Identified on: 4/24/2026

Mode: Standard