sedimentary

Chert (Nodule)

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs). Color: Dark gray to brownish-black. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.

Hardness: 7 (Mohs)
Color: Dark gray to brownish-black
Luster: Waxy to dull

Identified July 16, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs). Color: Dark gray to brownish-black. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary basins. Often found as nodules within limestone or chalk beds.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges. Used today in road construction, landscaping, and occasionally as a gemstone in the form of flint or jasper.

Geological facts

Chert was one of the most important materials for early humans because its conchoidal fracture produces razor-sharp edges. When struck against steel, it can produce sparks, leading to its use in flintlock firearms.

Field identification & locations

Identify by its waxy texture, extreme hardness (it will scratch glass), and shell-like (conchoidal) fracture patterns. Frequently found in riverbeds or eroded out of limestone cliffs.