sedimentary
Chalcedony (Agate and Jasper Pebbles)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Brown, orange, black, and green; Luster: Waxy to vitreous; Crystal Structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64
- Hardness
- 6
- Color
- Brown, orange, black, and green
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 Mohs; Color: Brown, orange, black, and green; Luster: Waxy to vitreous; Crystal Structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64
Formation & geological history
Formed through the deposition of silica from groundwater in cavities of volcanic or sedimentary rocks. These specimens are river-worn or beach-worn pebbles that have been naturally tumbled over time.
Uses & applications
Used for lapidary work, jewelry (beads, cabochons), collection, and as decorative river stones.
Geological facts
Agates and jaspers are both varieties of chalcedony; agates are typically translucent with banding, while jaspers are opaque. These river pebbles often travel hundreds of miles from their source ledge.
Field identification & locations
Look for rounded, smooth shapes with a waxy surface texture in stream beds or gravel pits. They are often more durable than the surrounding host rock, allowing them to accumulate in alluvial deposits.
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