sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Gray, black, or brown; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 7 on Mohs scale
Color: Gray, black, or brown
Luster: Waxy to dull

Identified July 9, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, black, or brown; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through the chemical precipitation of silica in groundwater within sedimentary host rocks like limestone.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) and fire-starting. Currently used in road surfacing, as an abrasive, and occasionally in jewelry as or a decorative stone.

Geological facts

Because of its conchoidal fracture pattern, chert breaks with extremely sharp edges, making it the primary material for prehistoric weaponry. High-quality black chert is often specifically referred to as Flint.

Field identification & locations

Identify in the field by its waxy texture, extreme hardness (it will scratch glass), and its characteristic shell-like (conchoidal) curved fractures. Commonly found as nodules in limestone or as smooth river pebbles.