sedimentary

Chert (Nodular Chert)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 (can scratch glass or steel). Color: Tan, brown, and cream with possible iron staining. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (has conchoidal fracture). Specific Gravity: 2.65.

Hardness: 6
Color: Tan, brown, and cream with possible iron staining
Luster: Waxy to dull

Identified June 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily through the replacement of calcium carbonate by silica in marine limestone or through the accumulation of siliceous organism remains (like diatoms or sponges). It is often found in prehistoric and Paleozoic sedimentary layers.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp edges. Modernly used as road base, decorative landscaping stone, and in ceramic manufacturing.

Geological facts

Flint is a variety of chert. Because of its hardness and chemical stability, chert is often found as smooth nodules in riverbeds long after the surrounding limestone has eroded away.

Field identification & locations

Identify by its hardness (cannot be scratched by a knife), waxy feel on smooth surfaces, and shell-like (conchoidal) fracture pattern. Commonly found in limestone outcrops and gravel beds.

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)

sedimentary

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