Agate

Physical Properties

Hardness: 6.5–7 (Mohs scale); Color: Variegated, tan/grey/blue-grey; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.60–2.65.

Formation & Geological History

Formed in cavities (vesicles) of volcanic rock or occasionally in sedimentary rock, where silica-rich groundwater precipitates in layers over millions of years. This specimen appears water-worn, likely from a stream or beach environment.

Uses & Applications

Used primarily for jewelry, lapidary art, decorative carvings, and in industrial applications like mortars and pestles due to its hardness and chemical resistance.

Geological Facts

Agate is named after the Achates River in Sicily where it was first discovered. Every agate is unique because the layers form according to the specific mineral impurities and pressure changes during its formation.

Field Identification & Locations

Identify in the field by its waxy appearance, translucency when held to light, and characteristic banding or cloud-like patterns. Common in gravel beds and along rocky shorelines.

Identified on: 4/25/2026

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