sedimentary
Banded Chert
Silicon Dioxide (SiO2)
Hardness: 7 Mohs; Color: Dark grey with tan/creamy bands; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); SG: 2.65
- Hardness
- 7 Mohs
- Color
- Dark grey with tan/creamy bands
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs; Color: Dark grey with tan/creamy bands; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); SG: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine environments; age varies from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools (arrowheads); currently used in decorative landscaping, jewelry (as river pebbles or cabochons), and as a silica source.
Geological facts
Also known as a 'Wishing Stone' when a single white band encircles the rock. Chert is extremely durable and can withstand significant water erosion, which rounded this specimen.
Field identification & locations
Identify by its hardness (scratches glass), waxy feel, and smooth curves if water-worn. Common on beaches and in riverbeds globally.
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