Granite Cobble (River Stone)

Physical Properties

Hardness: 6-7 on Mohs scale; Color: Mottled grey, white, and tan; Luster: Dull to vitreous; Crystal structure: Phaneritic (visible grains); Cleavage: None (fractures irregularly); Specific gravity: ~2.6-2.7

Formation & Geological History

Formed from the slow cooling of silica-rich magma deep underground. This specific specimen has been shaped and smoothed by water erosion in a high-energy environment like a river or beach over thousands of years.

Uses & Applications

Used primarily in landscaping, construction (as aggregate), and as decorative masonry. Polished versions are used for countertops and tiles.

Geological Facts

Granite is the primary component of the Earth's continental crust. Because it is so hard and durable, it is often the last material to break down as mountains erode, resulting in these rounded stones found in riverbeds.

Field Identification & Locations

Identify by its 'salt and pepper' appearance and hardness (it will scratch glass). Commonly found in glacial tills, riverbeds, and mountainous regions worldwide. Collectors look for unique mineral inclusions or garnets.

Identified on: 4/24/2026

Mode: Standard