sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Brown, tan, or wax-colored; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Brown, tan, or wax-colored
Luster: Waxy to dull

Identified June 25, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Brown, tan, or wax-colored; 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 marine environments; often found as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools and fire-starting; currently used in construction aggregate, road surfacing, and as a semi-precious gemstone in jewelry (Jasper varieties).

Geological facts

Chert has been used by humans for over 2 million years to make sharp-edged tools like arrowheads and knives because of it conchoidal fracture pattern.

Field identification & locations

Identify in the field by its waxy appearance, extreme hardness (it will scratch glass), and its tendency to break into sharp, curved flakes. Common in sedimentary basins worldwide.