Agate

Physical Properties

Hardness: 6.5–7 (Mohs scale); Color: Variegated bands of brown, white, and grey; Luster: Waxy to vitreous when polished; Crystal structure: Trigonal/Microcrystalline; Cleavage: None; Specific Gravity: 2.58–2.64

Formation & Geological History

Formed by the deposition of silica from groundwater in the cavities (vesicles) of igneous rocks or in sedimentary pockets. These layers form rhythmically over time.

Uses & Applications

Used primarily in jewelry (cabochons), ornamental carvings, burnishing tools for metalworking, and as precision bearings in laboratory balances.

Geological Facts

Ancient Greeks and Romans used agates for signet rings and amulets; the stone gets its name from the Achates River in Sicily where it was famously found in antiquity.

Field Identification & Locations

Identify by distinctive banding patterns and translucency. Commonly found in basaltic lava flows and gravel beds. Collectors look for unique 'eye' or 'fortification' patterns.

Identified on: 4/13/2026

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