mineral

Chalcedony (Agate/Chert variety)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Gray, tan, bluish-white; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline (Trigonal/Monoclinic); Cleavage: None/Conchoidal fracture; Specific Gravity: 2.6-2.64

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

Identified May 5, 2026More mineral →

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Physical properties

Formation & geological history

Formed as a chemical precipitate from silica-rich hydrothermal fluids or groundwater, often filling cavities in volcanic rocks or occurring as nodules in sedimentary limestone/dolomite.

Uses & applications

Used primarily in jewelry as gemstones, in lapidary arts for carvings/beads, and historically as tools (arrowheads/scrapers) due to its sharp conchoidal fracture.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen with a standard microscope. Agate and Carnelian are popular subspecies of chalcedony.

Field identification & locations

Identify by its waxy luster, smooth conchoidal (shell-like) fracture, and inability to be scratched by a steel knife. Common in volcanic regions and river gravels.

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