sedimentary
Banded Agate (Banded Chert / Jasper)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Dark grey, reddish-brown, and tan/white banding. Luster: Vitreous to waxy. Crystal Structure: Microcrystalline/Cryptocrystalline trigonal quartz. Cleavage: None (conchoidal fracture). Specific Gravity: ~2.6.
- Hardness
- 6
- Color
- Dark grey, reddish-brown, and tan/white banding
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Dark grey, reddish-brown, and tan/white banding. Luster: Vitreous to waxy. Crystal Structure: Microcrystalline/Cryptocrystalline trigonal quartz. Cleavage: None (conchoidal fracture). Specific Gravity: ~2.6.
Formation & geological history
Formed through silica precipitation from fluids depositing layer by layer in rock cavities or sedimentary environments, often associated with Precambrian iron formations or volcanic hosts.
Uses & applications
Polished for lapidary arts, jewelry components, wire-wrapping, or collected as tumbled decorative stones.
Geological facts
Banded agates and jasper/chert variants often preserve fine depositional layers formed over thousands of years, with iron oxide impurities creating distinct reddish hues.
Field identification & locations
Look for distinct fine parallel banding or striping on a smooth, hard surface. Commonly found along beaches, riverbeds, and gravel deposits worldwide, including Lake Superior and Brazil.
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