sedimentary

Chert (Flint)

Chert (Silicon Dioxide, SiO2)

Hardness: 7 on Mohs scale; Color: Gray, tan, or bluish-gray; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Gray, tan, or bluish-gray
Luster: Waxy to dull

Identified June 28, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, tan, or bluish-gray; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed as a chemical precipitate or through the replacement of limestone by silica-rich fluids. Often found as nodules within limestone or chalk beds. These specimens appear to be water-worn pebbles.

Uses & applications

Historically used for stone tools and weapons. Currently used as road aggregate, in glass making, and as a decorative stone in landscaping.

Geological facts

Chert has been used by humans for hundreds of thousands of years to create sharp-edged tools due to its conchoidal fracture pattern. It can create sparks when struck against steel.

Field identification & locations

Identify in the field by its hardness (cannot be scratched by a steel knife), its smooth, waxy texture, and its tendency to break with sharp, curved edges. Commonly found in riverbeds and sedimentary outcrops.