mineral

Quartz Cobble (River Rock)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale), Color: White to off-white with tan staining, Luster: Vitreous/Waxy when wet, Crystal Structure: Trigonal, Cleavage: None (Conchoidal fracture), Specific Gravity: 2.65

Identified June 25, 2026More mineral →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 7 (Mohs scale), Color: White to off-white with tan staining, Luster: Vitreous/Waxy when wet, Crystal Structure: Trigonal, Cleavage: None (Conchoidal fracture), Specific Gravity: 2.65

Formation & geological history

Formed primarily in igneous and metamorphic environments, this specimen was likely eroded from a vein and rounded into a cobble shape via water transport in a river or coastal environment over thousands of years.

Uses & applications

Commonly used in landscaping, decorative stone masonry, abrasive blasting, and as industrial silica source; well-rounded specimens are used as 'worry stones' or for tumbling.

Geological facts

Quartz is the second most abundant mineral in Earth's continental crust. Its durability and lack of cleavage are why it survives long journeys in riverbeds while softer minerals dissolve or break apart.

Field identification & locations

Identify by its hardness (it will scratch glass and steel), lack of cleavage, and translucent properties. Commonly found in riverbeds, glacial deposits, and beaches globally.