Quartz Pebble

Hardness: 7 (Mohs scale), Color: tan to milky white, Luster: waxy to vitreous (when polished), Crystal Structure: trigonal (not visible in pebble form), Cleavage: none (conchoidal fracture)

Formed from hydrothermal veins or as a constituent of igneous rocks, subsequently eroded and rounded by water transport in riverbeds or coastal environments. Likely millions of years old based on typical tectonic cycles.

Commonly used as decorative landscaping stone, in aquarium gravel, and as a source for high-purity silica in glass making or industrial abrasives. Smooth pebbles are also popular for worry stones and tumbling.

Quartz is the second most abundant mineral in Earth's continental crust. Its high hardness and chemical resistance allow it to survive erosion longer than most other minerals, explaining why most beach sand and river pebbles are composed of quartz.

Identify in the field by its hardness (it will scratch glass), lack of visible grains, and the fact it will not react with acid. Frequently found in riverbeds, glacial deposits, and along coastlines worldwide.