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

Identified June 27, 2026More sedimentary →

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Physical properties

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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