mineral

Chalcedony (River Pebble)

Silicon Dioxide (SiO2)

Hardness: 6.5–7 on the Mohs scale; Color: Milky white to translucent pale yellow; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline (Trigonal/Monoclinic); Cleavage: None; Specific Gravity: 2.58–2.64.

Hardness: 6
Color: Milky white to translucent pale yellow
Luster: Waxy to vitreous

Identified July 1, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica from water in cavities of volcanic or sedimentary rocks. This specimen is water-worn, likely tumbled in a river or beach environment over thousands of years.

Uses & applications

Commonly used for lapidary work, jewelry (beads and cabochons), and as a collector's stone. In history, it was used for seal stones and tools due to its toughness.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen under a normal microscope. It is the family name for stones like agate, jasper, and carnelian.

Field identification & locations

Identify in the field by its waxy appearance, lack of cleavage (conchoidal fracture), and inability to be scratched by a steel knife. Frequently found in riverbeds and gravel pits.