mineral

Banded Agate (with small Geode cavity)

Silicon Dioxide (SiO2) - Chalcedony variety

Hardness: 6.5–7 (Mohs scale); Color: White, gray, and brown concentric bands; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.58–2.64.

Hardness: 6
Color: White, gray, and brown concentric bands
Luster: Waxy to vitreous

Identified March 14, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica from groundwater into cavities (vesicles) within igneous volcanic rocks or sedimentary formations. As silica-rich fluids cool or evaporate, they create layered bands. This specimen likely dates from the Cenozoic to Mesozoic era.

Uses & applications

Commonly used in jewelry (cabochons, beads), decorative carvings, precision pendulums, and as sandpaper abrasives. Highly valued as a 'pocket stone' or display piece for mineral collectors.

Geological facts

Agates are named after the Achates River in Sicily where they were first found. The 'eye' or cavity in the center of this specimen indicates it is technically a 'geode' fragment, where the crystallization process did not completely fill the void.

Field identification & locations

Identify in the field by looking for translucent stones with visible Parallel or concentric banding when wet or backlit. Common locations include Brazil, Uruguay, and the Lake Superior region of the USA. Collectors look for high contrast in the bands and 'druzy' (sparkling) crystals in the center.

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