sedimentary

Chert (Flint)

Chert (Microcrystalline Quartz, SiO2)

Hardness: 7 on Mohs scale; Color: Gray, tan, and brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7. Highly durable and glass-like when broken.

Hardness: 7 on Mohs scale
Color: Gray, tan, and brown
Luster: Waxy to dull

Identified June 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from silica-rich fluids within limestone or chalk beds. Often found as nodules or pebbles tumbled by water.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) and starting fires. Modernly used in road construction, gravel, and occasionally as lapidary material for jewelry.

Geological facts

Flint is a variety of chert that was essential to human survival for millennia due to its ability to produce sparks when struck against steel and its sharp edges when fractured.

Field identification & locations

Identify in the field by its smooth, waxy texture, conchoidal (shell-like) fracture patterns, and its ability to scratch glass. Commonly found in stream beds, beaches, and within sedimentary rock outcrops.

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Sandstone or Siltstone

Arenite (if sandstone)

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Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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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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Sandstone

Arenite (primarily SiO2)

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