sedimentary

Chert (Jasper/Basalt River Pebble)

Silicon Dioxide (SiO2) or Microcrystalline Quartz

Hardness: 6.5-7 Mohs; Color: Dark grey, brown, olive-green; Luster: Waxy to dull; Crystal structure: Microcrystalline (hidden crystals); Cleavage: None (conchoidal fracture); Opaque to translucent edges.

Hardness: 6
Color: Dark grey, brown, olive-green
Luster: Waxy to dull

Identified July 11, 2026More sedimentary →

Explore Chert (Jasper/Basalt River Pebble) in the encyclopedia →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or river environments. This specific specimen appears to be water-worn, smoothed by fluvial (river) transport over thousands of years.

Uses & applications

Used historically for flint-knapping tools and weapons. Current uses include landscaping, road aggregate, and as a collector's specimen for tumbled stones.

Geological facts

Chert is a incredibly durable stone that resists weathering. Because of its hardness and ability to fracture into sharp edges, it was one of the most important stones used by prehistoric humans to create arrowheads and scrapers.

Field identification & locations

Identify by its 'waxy' texture when wet and its inability to be scratched by a steel knife. It is commonly found in riverbeds, glacial tills, and coastal beaches. Look for a smooth, rounded shape and a dull sheen.

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Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

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Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

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