Granite

Physical Properties

Hardness: 6-7 (Mohs scale); Color: Typically light-colored, but can be pink, white, gray, or black depending on mineralogy; Luster: Vitreous; Crystal structure: Phaneritic (coarse-grained); Cleavage: No true cleavage as a rock, but individual feldspar and mica crystals exhibit cleavage; Specific Gravity: 2.6-2.7 g/cm³.

Formation & Geological History

Formed from the slow crystallization of magma below Earth's surface during the intrusion of large igneous bodies (plutons). This slow cooling allows for the formation of large, visible mineral grains. Geological age varies widely, from Precambrian to recent, often associated with continental crust formation and mountain-building events.

Uses & Applications

Widely used in construction for countertops, flooring, curbing, building facades, and monuments due to its durability, aesthetic appeal, and resistance to weathering. Also used for decorative purposes and occasionally for engraving or sculpture.

Geological Facts

Granite is one of the most common intrusive igneous rocks and forms the core of many mountain ranges. It is the most abundant rock in the continental crust. The term 'granite' actually encompasses a range of felsic intrusive rocks. The various colors are due to different proportions of quartz (usually gray/white), feldspar (pink/white), mica (black/dark brown), and amphibole (black).

Field Identification & Locations

Identify in the field by its coarse-grained texture, often visible interlocking crystals (feldspar, quartz, mica), and typically light color. It is hard and resistant to scratching. Common locations include continental shield areas, cores of eroded mountain ranges, and batholiths. Tips for collectors: Look for freshly exposed outcrops or glacial erratics. Note the distinct mineral grains and their colors to appreciate its composition.

Identified on: 10/26/2025

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