sedimentary

Agate

Silicon dioxide (Chalcedony), SiO2

Hardness: 6.5 to 7 on the Mohs scale. Color: Varies widely including brown, red, grey, white, orange, and yellow due to impurities. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline quartz). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.58 to 2.64.

Hardness: 6
Luster: Waxy to vitreous

Identified August 6, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed mainly within cavities of volcanic and metamorphic rocks through the slow deposition of silica-rich groundwater solutions in concentric layers over millions of years.

Uses & applications

Used primarily in ornamental objects, jewelry, tumbled stones, carvings, and occasionally in precision instruments due to its durability.

Geological facts

Agates are among the oldest known gemstones, historically used in ancient civilizations for seals, signet rings, and protective amulets. The concentric banding records changes in the chemical composition of the fluids forming them.

Field identification & locations

Easily identified by its waxy luster, conchoidal fracture, and characteristic banding patterns. Commonly found globally in volcanic regions, riverbeds, and gravel deposits. Look for translucency at thin edges and high resistance to scratching.