mineral

Chalcedony (River Stone)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Gray, bluish-white; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (Trigonal/Monoclinic); Cleavage: None; Specific gravity: 2.58-2.64

Hardness: 6
Color: Gray, bluish-white
Luster: Waxy to vitreous

Identified April 7, 2026More mineral →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Gray, bluish-white; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (Trigonal/Monoclinic); Cleavage: None; Specific gravity: 2.58-2.64

Formation & geological history

Formed through the precipitation of silica from groundwater in volcanic cavities, sedimentary rocks, or hydrothermal veins. This specific specimen has been rounded and smoothed by water erosion in a river or coastal environment.

Uses & applications

Used in gemstone carving, jewelry making (cabochons), and as a collector's item. Historically used for making tools and seals.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen without a microscope. It comes in many varieties including agate, carnelian, and onyx.

Field identification & locations

Identify in the field by its waxy appearance, lack of visible crystals, and extreme hardness (it will scratch glass). Commonly found in dry riverbeds, beaches, and gravel pits.