mineral

Quartz Cobble

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Tan, cream, or milky white with some translucency; Luster: Vitreous to waxy (when polished by water); Crystal Structure: Hexagonal (trigonal); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Tan, cream, or milky white with some translucency
Luster: Vitreous to waxy (when polished by water)

Identified June 16, 2026More mineral →

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Physical properties

Formation & geological history

Formed usually in hydrothermal veins or as a primary constituent of igneous rocks. This specific specimen is a water-worn river cobble or 'pebble,' shaped by mechanical erosion in a high-energy environment like a stream or beach over millions of years.

Uses & applications

Used as decorative garden stone, in construction aggregates, as a source for silica in glassmaking and electronics, or as a pocket stone for collectors.

Geological facts

Quartz is the second most abundant mineral in Earth's continental crust. These rounded specimens are often referred to as 'river rocks' and have been smoothed by the constant tumbling against other rocks in moving water.

Field identification & locations

Identify by its hardness (it will scratch glass) and lack of cleavage. Look for smooth, rounded edges and a lack of visible grains, which distinguishes it from quartzite or sandstone. Found globally in riverbeds and coastal areas.