mineral
Chalcedony / Quartz Nodule (Agate Pebble)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: yellowish-grey to translucent white with subtle banding; Luster: waxy to vitreous; Crystal structure: Microcrystalline/Cryptocrystalline trigonal; Cleavage: none (conchoidal fracture).
- Hardness
- 6
- Color
- yellowish-grey to translucent white with subtle banding
- Luster
- waxy to vitreous
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: yellowish-grey to translucent white with subtle banding; Luster: waxy to vitreous; Crystal structure: Microcrystalline/Cryptocrystalline trigonal; Cleavage: none (conchoidal fracture).
Formation & geological history
Formed by the low-temperature deposition of silica from groundwater solution into cavities or fractures in host rocks, commonly basaltic or sedimentary formations.
Uses & applications
Popular for lapidary work, cabochon cutting, jewelry making, and beachcombing rock collections.
Geological facts
Chalcedony is composed of microscopic intergrowths of quartz and moganite. Water-worn pebbles often develop a distinctive translucent or waxy exterior when wet on beaches.
Field identification & locations
Identified by its microcrystalline texture, waxy luster when wet, translucent edges, and conchoidal fracture pattern. Common along coastal gravel beds, rivers, and volcanic regions worldwide.
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