mineral

Chalcedony (Agate/Chert variety)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale), Color: Yellowish-tan to white, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline (Trigonal/Monoclinic), Cleavage: None/Conchoidal fracture, Specific Gravity: 2.58–2.64

Hardness: 6

Identified May 24, 2026More mineral →

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Physical properties

Formation & geological history

Formed from the deposition of silica-rich groundwater in cavities of volcanic or sedimentary rocks. It often precipitates at low temperatures and can be found in various geological ages ranging from Precambrian to recent.

Uses & applications

Used primarily for jewelry (cabochons), ornamental carvings, stone tools (historically), and as a collector's specimen.

Geological facts

Chalcedony is one of the first materials humans used to make tools because of its hardness and the sharp edges produced by its conchoidal fracture. It is often found as a lining in geodes.

Field identification & locations

Identify in the field by its waxy luster, lack of visible crystals (cryptocrystalline), and its ability to scratch glass. It often occurs as nodules or botryoidal masses in sedimentary environments or volcanic vugs.

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