Granite Cobble

Physical Properties

Hardness: 6-7 on Mohs scale. Color: Spotted pink, white, and black. Luster: Dull to vitreous. Crystal structure: Phaneritic (coarse-grained). Cleavage: Varies by constituent mineral. Specific Gravity: 2.63 to 2.75.

Formation & Geological History

Formed from the slow cooling of silica-rich magma deep underground. This specific specimen is a water-worn cobble, indicating it was transported and eroded by water in a river or glacial environment.

Uses & Applications

Used widely in construction for countertops, floor tiles, and paving. Coarse river cobbles are often used in landscaping and as aggregate.

Geological Facts

Granite makes up the majority of the Earth's continental crust. The pink hues in this specimen come from potassium-rich orthoclase feldspar, while the darker flecks are likely hornblende or biotite mica.

Field Identification & Locations

Identify by its 'salt and pepper' appearance and coarse crystalline texture where individual minerals are visible to the naked eye. Commonly found in riverbeds, glacial tills, or mountainous outcrops worldwide.

Identified on: 4/30/2026

Mode: Standard