sedimentary
Chalcedony (Agate/Jasper mix)
Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Tan, brown, and translucent white; Luster: Waxy to vitreous; Structure: Microcrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Tan, brown, and translucent white
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 Mohs; Color: Tan, brown, and translucent white; Luster: Waxy to vitreous; Structure: Microcrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the deposition of silica from groundwater in cavities of volcanic or sedimentary rocks. This specific specimen appears to be a water-worn river pebble.
Uses & applications
Commonly used for lapidary work, jewelry (cabochons), and as decorative stones for collectors.
Geological facts
Chalcedony is a broad term that includes Agate (banded), Jasper (opaque), and Onyx. It has been used since the Bronze Age for making seals and jewelry.
Field identification & locations
Look for a waxy luster and translucent patches when held to light. Often found in riverbeds or gravel deposits where volcanic activity once occurred.
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