Banded Agate (Agatized Geode Slice)

Physical Properties

Hardness: 6.5-7 (Mohs scale); Color: Gray, tan, white, and translucent; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline (Trigonal); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.58-2.64.

Formation & Geological History

Formed through the deposition of silica from groundwater into cavities (vesicles) within igneous or sedimentary rocks. The bands represent different stages of mineral deposition over thousands of years as the chemistry of the water changed.

Uses & Applications

Used primarily in lapidary arts, jewelry (cabochons), interior decor, and as educational or geological specimens for collectors.

Geological Facts

Agate is a variety of chalcedony. This specific specimen shows a 'vug' or geode center, where the crystallization process was not completed, leaving a small hollow space lined with tiny crystals.

Field Identification & Locations

Identify in the field by looking for translucent, banded nodules often with a rough, weathered exterior but a colorful, glassy interior when broken. Commonly found in areas with volcanic activity or ancient riverbeds (e.g., Brazil, Uruguay, Lake Superior region).

Identified on: 4/25/2026

Mode: Standard