sedimentary
Banded Chert
Silicon dioxide (SiO2) with impurities
Hardness: 6.5-7 Mohs; Color: Tan, brown, green, and cream; Luster: Waxy to dull; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-2.8
- Hardness
- 6
- Color
- Tan, brown, green, and cream
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Tan, brown, green, and cream; Luster: Waxy to dull; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-2.8
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine environments, followed by lithification over millions of years. Banding often occurs due to rhythmic changes in sediment supply.
Uses & applications
Primarily collected as display specimens or lapidary material. Historically used for stone tools (arrowheads, scrapers) due to its sharp conchoidal fracture.
Geological facts
This specimen is a river-worn pebble where the banding has been exposed and smoothed by water action. Similar stones with distinctive patterns are sometimes called 'concretionary chert' or 'river jasper' by collectors.
Field identification & locations
Identify in the field by its waxy texture, inability to be scratched by a steel knife, and characteristic 'bulla' or concentric banding. Often found in riverbeds or coastal gravels.
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