Mineral

Quartz Cobble

Quartz (Silicon Dioxide, SiO2)

Hardness: 7 on Mohs scale; Color: Smoky grey to tan with white weathered rind; Luster: Vitreous to waxy (weathered surface is dull); Crystal Structure: Hexagonal (trigonal); Cleavage: None/Conchoidal fracture; Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Smoky grey to tan with white weathered rind
Luster: Vitreous to waxy (weathered surface is dull)

Identified June 12, 2026More mineral →

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Physical properties

Formation & geological history

Formed from silica-rich fluids in hydrothermal veins or as a primary constituent in igneous rocks. This specific specimen is a water-worn river stone or beach cobble, shaped by mechanical erosion over thousands of years.

Uses & applications

Used as industrial abrasive, in glass making, as a source for silicon, and in construction as aggregate. Smooth cobbles are often used in landscaping and interior design.

Geological facts

Quartz is the second most abundant mineral in Earth's continental crust. Its rounded shape indicates a long history of transport by water, likely from an ancient riverbed or glacial deposit.

Field identification & locations

Identify in the field by its hardness (cannot be scratched by a steel knife) and its smooth, rounded exterior often showing a 'bruised' or frosted white rind. It is found globally in riverbeds, beaches, and glacial till.