sedimentary

Chert (Flint)

Silicon Dioxide (SiO2) - Cryptocrystalline Quartz

Hardness: 7 (Mohs scale); Color: Dark grey to black (likely flint variety); Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (shows conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Dark grey to black (likely flint variety)
Luster: Waxy to dull

Identified April 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich marine organisms (like diatoms or radiolarians) or through chemical precipitation in limestone/dolomite cavities. Common in Phanerozoic sedimentary sequences.

Uses & applications

Historically used for making stone tools (arrowheads, knives) due to sharp edges; used as a fire starter when struck against steel; road aggregate and decorative landscaping.

Geological facts

Flint is the most common name for dark-colored chert. It has been vital to human technology since the Stone Age and was a primary industrial material for fire-starting before matches.

Field identification & locations

Identify by its characteristic 'curved' conchoidal fracture patterns and inability to be scratched by a steel knife. Commonly found as nodules in limestone beds or as water-worn pebbles in riverbeds.

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