mineral

Milky Quartz (Water-Worn Cobble)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: White to Opaque (due to microscopic fluid inclusions); Luster: Vitreous to greasy; Crystal Structure: Trigonal (hexagonal system); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: White to Opaque (due to microscopic fluid inclusions)
Luster: Vitreous to greasy

Identified March 19, 2026More mineral →

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Physical properties

Formation & geological history

Formed from silica-rich hydrothermal fluids cooling in veins or from the crystallization of magma. This specific specimen has been chemically and physically weathered and polished into a smooth cobble shape by water action in a river, stream, or beach environment.

Uses & applications

Used in glassmaking, abrasives, and as a source of silicon for electronics. In cobble form, it is widely used for decorative landscaping, construction aggregate, and as 'pocket stones' for casual collectors.

Geological facts

Milky quartz gets its cloudy appearance from minute bubbles of gas or liquid trapped during crystal growth. It is the most common variety of crystalline quartz found on Earth’s crust.

Field identification & locations

Identify in the field by its inability to be scratched by a steel knife (7 hardness) and its lack of cleavage. Look for it in gravel bars, riverbeds, and glacial till. It is often the last mineral remaining after others have eroded away due to its high chemical stability.

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