Agate

Physical Properties

Hardness: 6.5–7 on Mohs scale; Color: Milky white, cream, tan; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Fracture: Conchoidal; Specific gravity: 2.58–2.64.

Formation & Geological History

Formed in cavities of volcanic rocks (basalt or andesite) or sedimentary rocks when silica-rich groundwater precipitates over time, creating concentric layers. These can range from hundreds of millions of years old to relatively recent geological formations.

Uses & Applications

Used primarily in lapidary arts for jewelry, decorative carvings, bookends, and ornaments. Historically used for making precision bearings and mortars and pestles due to its hardness.

Geological Facts

Agates are unique because no two are exactly alike. They are named after the Achates River in Sicily where they were first found. This specimen shows 'fairburn' or fortification-like banding patterns common in chalcedony nodules.

Field Identification & Locations

Identify in the field by its waxy texture, translucency when held to light, and characteristic conchoidal fracture (curved, glass-like breaks). Common in river beds, deserts, and volcanic regions worldwide.

Identified on: 4/28/2026

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