mineral
Chalcedony (Agate/Carnelian)
Silicon Dioxide (SiO2)
Hardness: 6.5-7.0 (Mohs scale), Color: translucent white to amber/yellow, Luster: waxy to vitreous, Crystal structure: cryptocrystalline (hexagonal/trigonal), Cleavage: none (conchoidal fracture)
- Hardness
- 6
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Physical properties
Hardness: 6.5-7.0 (Mohs scale), Color: translucent white to amber/yellow, Luster: waxy to vitreous, Crystal structure: cryptocrystalline (hexagonal/trigonal), Cleavage: none (conchoidal fracture)
Formation & geological history
Formed by the deposition of silica from groundwater in cavities of igneous and sedimentary rocks. Often found as nodules or vein fillings in volcanic ash or old lava flows.
Uses & applications
Used primarily in lapidary work for jewelry, decor, and as semi-precious gemstones. Historically used for making tools and seals.
Geological facts
Chalcedony was often used in ancient Rome to carve seals because wax does not stick to it. Agate is technically a banded variety of chalcedony.
Field identification & locations
Identify by its waxy luster, translucency, and smoothness. Common in riverbeds and volcanic regions like the American West, Brazil, and India.
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