sedimentary
Banded Chert (River Jasper)
Silicon Dioxide (SiO2) with impurities
Hardness: 6.5-7 Mohs; Color: Brown, tan, and olive green banding; Luster: Waxy to vitreous when wet; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Brown, tan, and olive green banding
- Luster
- Waxy to vitreous when wet
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Physical properties
Hardness: 6.5-7 Mohs; Color: Brown, tan, and olive green banding; Luster: Waxy to vitreous when wet; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich microfossils or chemical precipitation from hydrothermal fluids in marine environments. The banding represents pulse-like changes in mineral impurities during deposition over millions of years.
Uses & applications
Used primarily as decorative specimens, lapidary material for cabochons, landscaping, and historically for stone tools due to its sharp edges when fractured.
Geological facts
Chert is so durable that it often survives long-distance transport in rivers and glacial till, which is likely why this specimen appears water-worn. It is a main component of flint.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), its smooth waxy feel, and its distinct conchoidal (shell-like) fracture patterns. Frequently found in riverbeds and gravel pits.
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