mineral

Chalcedony (River Stone)

Microcrystalline Quartz (SiO2)

Hardness: 6.5–7 Mohs; Color: Tan, brown, and translucent grey; Luster: Waxy to vitreous; Crystal structure: Trigonal/Monoclinic (cryptocrystalline); Cleavage: None; Specific Gravity: 2.6–2.64

Hardness: 6
Color: Tan, brown, and translucent grey
Luster: Waxy to vitreous

Identified March 28, 2026More mineral →

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Physical properties

Hardness: 6.5–7 Mohs; Color: Tan, brown, and translucent grey; Luster: Waxy to vitreous; Crystal structure: Trigonal/Monoclinic (cryptocrystalline); Cleavage: None; Specific Gravity: 2.6–2.64

Formation & geological history

Formed from the precipitation of silica-rich groundwater in cavities of igneous or sedimentary rocks. This specific specimen shows significant water-wear, indicating it was transported by a river or stream over a long geological period.

Uses & applications

Common varieties are used for jewelry (cabochons), stone tumbling, aquarium decor, and lapidary art. Historically used for making tools like scrapers and arrowheads due to its conchoidal fracture.

Geological facts

Chalcedony is actually composed of two different minerals: quartz and moganite. The brown and dark spots in this specimen are likely iron or manganese oxide inclusions.

Field identification & locations

Identify in the field by its translucency (hold to light), waxy texture, and lack of visible grains. It cannot be' scratched by a steel knife. Commonly found in gravel beds, riverbanks, and volcanic regions.

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