mineral

River Quartz Pitting/Cobble

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale (can scratch glass). Color: Milky white to light grey with earthy surface staining. Luster: Vitreous when broken, dull/waxy when weathered. Crystal structure: Hexagonal/Trigonal (though rounded here). Cleavage: None (conchoidal fracture).

Hardness: 7 on Mohs scale (can scratch glass)
Color: Milky white to light grey with earthy surface staining
Luster: Vitreous when broken, dull/waxy when weathered

Identified March 5, 2026More mineral →

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Physical properties

Formation & geological history

Formed through hydrothermal processes in igneous veins or metamorphic environments. This specific specimen has undergone secondary mechanical weathering (rounding) in a high-energy aquatic environment like a riverbed or stream over thousands of years.

Uses & applications

Used industrially as an abrasive, in glass manufacturing, and in construction. Rounded cobbles are often used in landscaping and xeriscaping. Not valuable as jewelry in this raw, weathered state.

Geological facts

Quartz is the second most abundant mineral in Earth's continental crust. Rounded pieces like this are known as 'river rocks' or 'cobbles' and their smooth shape is the result of 'abrasion'—the process of rocks hitting each other and being worn down by water flow.

Field identification & locations

Identify by its weight and hardness; try to scratch a glass bottle with a sharp edge of the rock—if it scratches, it is likely quartz. Found globally in riverbanks, glacial tills, and beaches. Collectors look for pieces with internal clarity or unique inclusions.