sedimentary

Chert (Nodule)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Tan, white, and gray; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Tan, white, and gray
Luster: Waxy to dull

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Tan, white, and gray; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed through the chemical precipitation of silica-rich fluids within limestone or chalk beds. Often contains microfossils and forms as nodules or bedded layers in marine sedimentary environments.

Uses & applications

Historically used for stone tools (arrowheads/scrapers) due to its sharp edges; used today in road construction, as an abrasive, and by hobbyist flintknappers.

Geological facts

Chert has been used by humans for over 2 million years to create tools. Flint is a specific dark variety of chert. It can produce sparks when struck against steel, making it useful for fire-starting.

Field identification & locations

Identify by its waxy luster, extreme hardness (can scratch glass), and conchoidal (shell-like) fracture patterns. Look for it as nodules protruding from weathered limestone outcrops.