Agate

Physical Properties

Hardness: 6.5-7 (Mohs scale); Color: Variegated reds, oranges, and tans with visible banding; Luster: Waxy to vitrous; Crystal structure: Trigonal (microcrystalline quartz/chalcedony); Cleavage: None, exhibits conchoidal fracture.

Formation & Geological History

Formed in cavities of volcanic or metamorphic rocks when silica-rich groundwater deposits layers of chalcedony. The banding represents different stages of mineral deposition over thousands to millions of years.

Uses & Applications

Used in gemstone carving, jewelry (cabochons), precision bearings, and laboratory equipment due to its hardness and resistance to acids. Popular as a lapidary and collector's material.

Geological Facts

The banding in agates is often so fine that a single millimeter can contain thousands of individual layers. Agate was highly valued by ancient Greeks for talismans and seal stones.

Field Identification & Locations

Identify by looking for translucent areas, concentric or wavy banding, and a waxy texture. Commonly found in riverbeds, glacial deposits, and volcanic field tailings.

Identified on: 4/21/2026

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