Agate Geode

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Gray, white, and translucent; Luster: Vitreous to waxy; Crystal structure: Trigonal/Microcrystalline; Cleavage: None; Specific Gravity: 2.58-2.64

Formation & Geological History

Formed in cavities or vesicles of volcanic rock (basalt) or sedimentary rock. Silica-rich fluids percolate into these voids, depositing layers of chalcedony over millions of years starting from the Eocene to recent epochs.

Uses & Applications

Polished specimens are used for home decor, jewelry cabochons, metaphysical practices, and as collectibles. Industrially, high-quality chalcedony can be used for precision mortars and pestles.

Geological Facts

This specimen features a 'water-line' or horizontal agate banding, indicating the orientation of the geode while it was forming. Agates are the state rock of several US states including Minnesota and South Dakota.

Field Identification & Locations

Identify in the field by looking for rounded nodules with a rough, 'cauliflower-like' exterior in volcanic ash beds or gravel deposits. Common in Brazil, Uruguay, and the western United States.

Identified on: 5/3/2026

Mode: Standard