mineral

Banded Chalcedony (Agate)

Silicon Dioxide (SiO2) - Cryptocrystalline Quartz

Hardness: 6.5-7 (Mohs scale); Color: Variegated brown, tan, and white bands; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58–2.64

Hardness: 6
Color: Variegated brown, tan, and white bands
Luster: Waxy to vitreous

Identified March 28, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica from groundwater in cavities within igneous rocks (often volcanic or metamorphic host rocks). The bands result from rhythmic crystallization and variations in mineral impurities over time.

Uses & applications

Used primarily in lapidary arts for jewelry, beads, and cabochons. Historically used for making mortars and pestles and hard-wearing industrial bearings due to its toughness.

Geological facts

Agate bands can sometimes be so thin that up to 17,000 layers can be found in a single inch. This specific specimen appears to be a 'river rock' or 'glacier-worn' pebble, where natural water action has polished the surface.

Field identification & locations

Identify in the field by its waxy appearance when wet, translucency at the edges, and characteristic banding. Commonly found in riverbeds, glacial till, and gravel pits across North America, particularly in the Great Lakes region and the Pacific Northwest.

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