sedimentary

Chert (Jasper/Flint variant)

Microcrystalline quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Grayish-brown to olive; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 6
Color: Grayish-brown to olive
Luster: Waxy to vitreous

Identified June 30, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. These specimens are often hundreds of millions of years old, typically found in nodules within limestone or chalk beds.

Uses & applications

Historically used for stone tools (arrowheads/scrapers) due to its sharp edges when fractured. Modernly used in construction aggregate, road surfacing, and as a semi-precious gemstone when colorful (Jasper).

Geological facts

Chert was one of the most vital materials for early humans; its ability to produce a predictable conchoidal fracture allowed for the creation of sophisticated tools and weaponry.

Field identification & locations

Identify in the field by its hardness (will scratch glass), waxy texture, and shell-like (conchoidal) fracture patterns. Look for it in riverbeds or eroding out of sedimentary rock layers.

Other sedimentary specimens

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Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

sedimentary

Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

sedimentary

Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary

Sandstone

Arenite (primarily SiO2)

sedimentary