Granite Cobble

Physical Properties

Hardness: 6-7 on Mohs scale; Color: Mottled grey, pink, and tan with iron-oxide staining; Luster: Dull (weathered) to vitreous (on fresh breaks); Structure: Phaneritic (visible crystals); Cleavage: None (fractures irregularly).

Formation & Geological History

Formed from the slow cooling of silica-rich magma deep underground (intrusive). The rounded shape is the result of mechanical weathering and transport by water in a high-energy environment like a river or shoreline.

Uses & Applications

Used primarily as construction aggregate, decorative landscaping stone, or as a source of crushed stone for road bases.

Geological Facts

Granite is the primary component of Earth's continental crust. This specific specimen shows 'desert varnish' or iron-oxide staining on its surface due to exposure to the elements.

Field Identification & Locations

Identify in the field by its speckled 'salt and pepper' appearance and its extreme hardness; it will easily scratch glass and cannot be scratched by a steel knife. Commonly found in glacial tills and riverbeds.

Identified on: 5/1/2026

Mode: Standard