mineral

Chalcedony (Quartz Pebbles)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Translucent white to milky grey; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.58-2.64

Hardness: 6
Color: Translucent white to milky grey
Luster: Waxy to vitreous

Identified June 19, 2026More mineral →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Translucent white to milky grey; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.58-2.64

Formation & geological history

Formed from the deposition of silica from water in cavities or as nodules in volcanic and sedimentary rocks. These specimens appear to be water-worn pebbles from a river or beach environment.

Uses & applications

Used in gemstone carving, lapidary arts, jewelry (as cabochons), and historically for toolmaking (flint/chert varieties).

Geological facts

Chalcedony is a cryptocrystalline form of silica. It was once thought to be a mixture of quartz and moganite, but is now treated as a distinct variety of quartz with a fibrous microstructure.

Field identification & locations

Identify by its waxy luster, translucency, and inability to be scratched by a steel knife. Common in gravel beds and along coastlines near volcanic outcrops.