mineral

Banded Agate (River Stone)

Agate (Silicon Dioxide - SiO2)

Hardness: 6.5–7 on Mohs scale; Color: Translucent grey, tan, and brown with concentric bands; Luster: Vitreous to waxy (when polished/worn); Crystal structure: Trigonal/Microcrystalline (Cryptocrystalline quartz); Cleavage: None, exhibits conchoidal fracture.

Hardness: 6
Color: Translucent grey, tan, and brown with concentric bands
Luster: Vitreous to waxy (when polished/worn)

Identified March 30, 2026More mineral →

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Physical properties

Formation & geological history

Formed as a secondary mineral in volcanic or sedimentary rock cavities (geodes) through the deposition of silica-rich groundwaters. This specific specimen appears to be a 'river stone' or 'cobble' that has been naturally tumbled and rounded by water action over geological time.

Uses & applications

Commonly used in lapidary arts, jewelry (cabochons), and as decorative polished stones. In industry, due to its hardness and chemical resistance, it is used to make mortars and pestles for laboratories.

Geological facts

Agate is named after the Achates River in Sicily where it was first discovered in ancient times. The distinct banding is caused by rhythmic crystallization during the filling of the stone's host cavity.

Field identification & locations

Identify in the field by its translucency (when held to light), concentric banding patterns, and extreme hardness (it will scratch glass). Commonly found in riverbeds, beaches, and areas with ancient volcanic activity like the Lake Superior region or parts of Brazil.

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