sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Cream, tan, gray; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Cream, tan, gray
Luster: Waxy to dull

Identified June 19, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Cream, tan, gray; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed from the accumulation of siliceous remains of marine organisms or through chemical precipitation of silica-rich fluids in limestone or chalk beds. Commonly found in sedimentary basins worldwide.

Uses & applications

Historically used for stone tools and fire-starting. Currently used in road construction, as an abrasive, and for knapped decorative items.

Geological facts

Chert has a conchoidal fracture which creates razor-sharp edges, making it the primary material for prehistoric arrowheads and spear tips. It is also sparks when struck against steel.

Field identification & locations

Identify by its smooth, waxy feel and shell-like (conchoidal) breakage patterns. It is much harder than steel and cannot be scratched by a knife. Often found as nodules within limestone.