Agate (Banded Chalcedony)

Physical Properties

Hardness: 6.5–7 on the Mohs scale; Color: Banded layers of grey, white, and brown; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline (Trigonal); Cleavage: None; Specific Gravity: 2.58–2.64.

Formation & Geological History

Formed primarily within volcanic and metamorphic rocks. It develops as silica-rich groundwater fills cavities (vesicles) in igneous rocks, depositing layers of chalcedony over thousands of years.

Uses & Applications

Used extensively in jewelry (cabochons), interior decor, burnishing tools, and laboratory equipment like mortars and pestles due to its hardness and resistance to acids.

Geological Facts

Agate is named after the Achates River in Sicily where it was first discovered. The colorful bands are caused by traces of iron, manganese, or other mineral impurities during the deposition process.

Field Identification & Locations

Identify in the field by its characteristic concentric banding, waxy texture, and conchoidal (shell-like) fracture. Commonly found in river beds or areas with ancient volcanic activity like Brazil, India, and the Lake Superior region.

Identified on: 4/17/2026

Mode: Standard