sedimentary
Banded Agate (River Pebble)
Silicon Dioxide with impurities (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Tan, brown, and cream concentric bands; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64.
- Hardness
- 6
- Color
- Tan, brown, and cream concentric bands
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Tan, brown, and cream concentric bands; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64.
Formation & geological history
Formed as secondary deposits in volcanic rock cavities or sedimentary geodes through the deposition of silica-rich groundwater. This specimen shows significant river-wear or tumble-smoothing. Geological age varies from 20 million to over 1 billion years depending on location.
Uses & applications
Polishing for lapidary use, ornamental stones, metaphysical collecting, and jewelry making.
Geological facts
Agate bands are formed by the periodic precipitating of silica from aqueous solution. Each layer represents a different pulse of mineral-rich water entering a void in the earth.
Field identification & locations
Identify by looking for distinct concentric banding patterns and a translucency when held to light. Commonly found in riverbeds, glacial tills, and volcanic regions like the Lake Superior area or Brazil.
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