mineral

Quartz Pebble (Chalcedony/Agate variety)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Translucent tan to smoky grey with iron inclusions; Luster: Vitreous to waxy (especially when water-worn); Crystal structure: Hexagonal/Trigonal (Cryptocrystalline); Cleavage: None (Conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Translucent tan to smoky grey with iron inclusions
Luster: Vitreous to waxy (especially when water-worn)

Identified March 7, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the precipitation of silica from groundwater in cavities of volcanic or sedimentary rocks. This specific specimen appears to be a water-worn river pebble, likely millions of years old, weathered out of its host matrix and rounded by fluvial erosion.

Uses & applications

Common varieties are used for lapidary work (tumbling/polishing), aquarium gravel, and industrial abrasives. High-purity quartz is used in glassmaking and electronics.

Geological facts

Quartz is the second most abundant mineral in Earth's continental crust. Because of its high hardness and chemical stability, it often survives long after the surrounding rock has eroded away, forming common river and beach pebbles.

Field identification & locations

Identify in the field by its translucency and ability to scratch glass (hardness of 7). Most frequently found in riverbeds, glacial tills, and along coastlines. Collectors look for unique inclusions or banding (which would classify it as an agate).

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