sedimentary

Chert (Jasper/Jasperoid)

Chert (chemically precipitated microcrystalline Quartz, SiO2)

Hardness: 6.5–7 (Mohs); Color: Dark brown to black with tan/yellowish streaks; Luster: Waxy to dull (on weathered surfaces); Crystal structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.6–2.7

Hardness: 6
Color: Dark brown to black with tan/yellowish streaks
Luster: Waxy to dull (on weathered surfaces)

Identified April 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria) or chemical precipitation from hydrothermal fluids in sedimentary environments. Its age can range from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools (flintknapping); currently used in landscaping, as a gemstone (when colorful labels like Jasper are applied), and in concrete aggregate.

Geological facts

Chert is so hard it can scratch glass and steel. It was one of the most important commodities in human prehistory because it breaks into razor-sharp edges used for arrows and knives.

Field identification & locations

Identify by its waxy luster, extreme hardness, and 'smooth' curved fractures. Common in riverbeds as rounded pebbles or as nodules within limestone or shale layers.

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Sandstone or Siltstone

Arenite (if sandstone)

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Sandstone

Arenite (primarily SiO2)

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone (Quartz-rich)

Arenite (SiO2)

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Sandstone (with man-made markings)

Arenite (composed primarily of Quartz, SiO2)

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