mineral

Quartz Pebble (Milky and Gray)

Quartz (Silicon Dioxide, SiO2)

Hardness: 7 on the Mohs scale (scratches glass); Color: Opaque white to smoky gray with inclusions; Luster: Vitreous to greasy (waxy); Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on the Mohs scale (scratches glass)
Color: Opaque white to smoky gray with inclusions
Luster: Vitreous to greasy (waxy)

Identified March 8, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the cooling of silica-rich magma or through hydrothermal precipitation in veins. These pebbles are typically older than 100 million years, having been smoothed and rounded over time by water transport in rivers, glaciers, or coastal environments.

Uses & applications

Quartz is used industrially for glassmaking, abrasives, and electronics. Rounded pebbles are popular for landscaping, aquarium decor, and as 'river stones' for decorative paths. High-quality specimens are used in lapidary for tumbling and cabochon cutting.

Geological facts

Quartz is the second most abundant mineral in Earth's continental crust. Because of its hardness and chemical stability, it is the primary component of most beach sand worldwide. It demonstrates piezoelectricity, meaning it can generate an electric charge under mechanical stress.

Field identification & locations

Identify in the field by its hardness (it will easily scratch a steel knife or glass) and its lack of cleavage (it breaks in irregular, curved shards like glass). Found globally in river beds, moraines, and shorelines. Common in granite-rich regions and sedimentary basins.

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