Agate (or Chalcedony)

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown, tan, and orange patches; Luster: Waxy to vitreous; Crystal Structure: Trigonal (cryptocrystalline); Cleavage: None; Specific Gravity: 2.58-2.64.

Formation & Geological History

Formed as secondary deposits in volcanic rock cavities or sedimentary rocks. Silica-rich fluids precipitate in layers over long geological periods, often millions of years old.

Uses & Applications

Used primarily for jewelry (cabochons), lapidary art, decorative carvings, and as a collectible specimen.

Geological Facts

Agate is a variety of chalcedony characterized by its microcrystalline structure. It has been used for over 3,000 years for gemstone and ornamental purposes.

Field Identification & Locations

Identify by its waxy texture, conchoidal fracture (curved breaks), and hardness which avoids scratching by a steel blade. Commonly found in riverbeds, gravel pits, and volcanic regions.

Identified on: 4/30/2026

Mode: Standard