mineral

Agate

Silicon dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale), Color: Pale yellow-grey to translucent, Luster: Vitreous to waxy, Crystal structure: Trigonal/Microcrystalline, Cleavage: None, Specific gravity: 2.58-2.64

Hardness: 6

Identified May 13, 2026More mineral →

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Physical properties

Hardness: 6.5-7 (Mohs scale), Color: Pale yellow-grey to translucent, Luster: Vitreous to waxy, Crystal structure: Trigonal/Microcrystalline, Cleavage: None, Specific gravity: 2.58-2.64

Formation & geological history

Formed as a secondary mineral in volcanic cavities (vesicles) through the deposition of silica from groundwater. Usually Cretaceous to Tertiary in age.

Uses & applications

Used primarily for lapidary arts, jewelry (cabochons), burnishing tools, and as ornamental display pieces.

Geological facts

Agate is a variety of chalcedony. This specimen demonstrates the typical 'frosted' or tumbled outer rind common in river-worn or beach-collected stones.

Field identification & locations

Look for a waxy luster and conchoidal (shell-like) fracture. Found worldwide in volcanic regions, notably Brazil, Uruguay, and the Lake Superior region in the US.