mineral

Chalcedony (Agate/Chert variety)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale), Color: White, translucent gray, or tan, Luster: Waxy to vitreous, Crystal structure: Trigonal/Microcrystalline, Cleavage: None (Conchoidal fracture), Specific Gravity: 2.58-2.64

Hardness: 6

Identified June 13, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica from groundwater in cavities of igneous rocks or as nodules in sedimentary rocks like limestone. It can form at relatively low temperatures.

Uses & applications

Used primarily in lapidary work, jewelry (beads, cabochons), and as a collector's specimen. Historically used for making tools and weapons due to its sharp conchoidal fracture.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen without high magnification. It often forms the base material for agates and jaspers.

Field identification & locations

Identify in the field by its waxy luster, lack of visible crystals, and hard surface that cannot be scratched by a steel knife. Frequently found in desert regions, riverbeds, and volcanic ash deposits.

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Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

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Epidote

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Nephrite Jade

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Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

Biotite Schist

Biotite-rich Schist [K(Mg,Fe)3AlSi3O10(F,OH)2]

metamorphic