sedimentary

Chert (Jasper)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: brown, tan, and reddish-tan; Luster: waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: approx. 2.65.

Hardness: 6
Color: brown, tan, and reddish-tan
Luster: waxy to dull

Identified July 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via the accumulation of silica-rich microfossils or chemical precipitation from groundwater within sedimentary layers. This specimen shows significant rounding typical of fluvial (river) or glacial transport.

Uses & applications

Historically used for stone tools (flintknapping) due to its sharp edges when broken; currently used as an ornamental stone, for landscaping, or as a lapidary material for polishing.

Geological facts

Chert is so durable that it often remains in riverbeds long after the surrounding softer limestone or chalk has eroded away. The reddish hues in this specimen are likely due to iron oxide impurities.

Field identification & locations

Identify by its smooth, waxy texture and distinctive shell-like (conchoidal) fracture scars. It will scratch glass but cannot be scratched by a steel knife. Common in the Alpine foreland and Danube basin regions of Bavaria.