sedimentary

Chert (Jasper/Flint variety)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Brown, yellow, and orange due to iron oxide staining; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Brown, yellow, and orange due to iron oxide staining
Luster: Waxy to dull

Identified June 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) or by chemical precipitation in marine or groundwater environments. These river-worn specimens are typically from the Paleozoic or Mesozoic eras.

Uses & applications

Historical use for stone tools and arrowheads due to its sharp edges when broken. Today used as aquarium decor, in landscaping, as road aggregate, and as minor semi-precious gemstones when polished.

Geological facts

Chert is so durable that it often survives millions of years of river transport and weathering that destroys other rocks. It is chemically identical to quartz but has a different internal structure.

Field identification & locations

Identify in the field by its smooth, waxy texture when wet and its tendency to break with sharp, curved (conchoidal) edges. Look for it in riverbeds or gravel pits where water has rounded the stones.

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Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

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Sandstone

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone Grain

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Shale or Slaty Mudstone

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