sedimentary
Banded Chert (Jasper) River Pebble
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Tan, brown, and grey banding; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Tan, brown, and grey banding
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Tan, brown, and grey banding; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed as a chemical precipitate or through the replacement of limestone by silica-rich fluids. This specimen is a water-worn pebble, likely eroded from ancient sedimentary beds and smoothed over thousands of years in a river environment.
Uses & applications
Commonly used as decorative gravel, in lapidary work (polishing and tumbling), and historically used by indigenous people for stone tools due to its sharp fracture edges.
Geological facts
Chert and Jasper are varieties of chalcedony. The banding is often caused by the rhythmic precipitation of iron oxides or other impurities during the silica deposition process.
Field identification & locations
Identify in the field by its smooth texture, hardness (it will scratch glass), and characteristic banding. Often found in riverbeds, glacial tills, or coastal beaches.
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