mineral
Banded Chalcedony (Agate)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs); Color: translucent white to amber; Luster: waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: none; Fracture: conchoidal
- Hardness
- 6
- Color
- translucent white to amber
- Luster
- waxy to vitreous
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Physical properties
Hardness: 6.5-7 (Mohs); Color: translucent white to amber; Luster: waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: none; Fracture: conchoidal
Formation & geological history
Forms primarily in volcanic and sedimentary rocks where silica-rich groundwater fills cavities and precipitates in layered deposits over thousands of years.
Uses & applications
Used widely in lapidary work, jewelry making, ornamental carvings, and as a collector's specimen. Historically used for making tools and seals.
Geological facts
The banding in agate is caused by periodic changes in the concentration of silica and impurities during its formation inside volcanic vesicles.
Field identification & locations
Identify by its waxy texture, translucency, and conchoidal fracture. Often found as nodules in stream beds or weathered volcanic landscapes.
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Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
sedimentary
Schist
Schist
Metamorphic
Epidote
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metamorphic
Gypsum (variety Selenite or Alabaster)
Calcium sulfate dihydrate (CaSO4·2H2O)
Mineral
Nephrite Jade
Nephrite
Mineral/Rock
Banded Gneiss (River Rock/Pebble)
Gneiss (specifically a banded variety often found as a river rock)
Metamorphic Rock