sedimentary
Banded Agate (River-worn Pebble)
Cryptocrystalline Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs); Color: Waxy brown, honey, and white bands; Luster: Waxy to vitreous; Crystal Structure: Hexagonal (cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58–2.64.
- Hardness
- 6
- Color
- Waxy brown, honey, and white bands
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Waxy brown, honey, and white bands; Luster: Waxy to vitreous; Crystal Structure: Hexagonal (cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58–2.64.
Formation & geological history
Formed by the deposition of silica from groundwater in the cavities of igneous rocks. Over geological time, these nodules erode and are transported by water, resulting in the smooth, rounded surface seen here.
Uses & applications
Commonly used in jewelry for cabochons, lapidary art, tumble-polishing, and as decorative collection specimens.
Geological facts
The term agate comes from the Achates River in Sicily where they were first found. Every agate is unique because the banding represents changes in the chemistry of the silica-rich fluids over time.
Field identification & locations
Identify by its waxy luster, translucency when held to light, and characteristic concentric or parallel banding. Commonly found in riverbeds, lake shores, and gravel pits.
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