mineral

Quartz (Milk Quartz Cobble)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale), Color: White to off-white/tan, Luster: Vitreous to greasy, Crystal structure: Trigonal (often massive in cobbles), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Identified April 21, 2026More mineral →

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Physical properties

Formation & geological history

Formed from silica-rich hydrothermal fluids or within igneous pegmatites. This specific specimen is likely a water-worn or weathered cobble from an alluvial deposit, potentially millions of years old.

Uses & applications

Used in glassmaking, electronics (piezoelectric properties), abrasives, and as a common decorative landscape stone. High-purity quartz is essential for making silicon wafers for semiconductors.

Geological facts

Quartz is the second most abundant mineral in Earth's continental crust. Its name comes from the German word 'quarz'. It remains chemically stable under most surface conditions, which is why it often survives as rounded river stones long after other minerals have weathered away.

Field identification & locations

Identify in the field by its hardness (cannot be scratched by a steel nail), lack of cleavage, and translucent look. Common in riverbeds, mountain outcroppings, and beach gravels world-wide.