sedimentary

Chert (Flint)

Chert (Microcrystalline Quartz, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: typically grey, black, or brown; Luster: waxy to dull; Structure: microcrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: typically grey, black, or brown
Luster: waxy to dull

Identified February 25, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: typically grey, black, or brown; Luster: waxy to dull; Structure: microcrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed by the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or through the precipitation of silica in groundwater within limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons; currently used in construction aggregate, road surfacing, and as a starting material for flint-striking fire starters.

Geological facts

Flint is a variety of chert that was essential to human evolution for creating sharp-edged tools and sparks for fire. It produces a glass-like conchoidal fracture which allows for precision knapping.

Field identification & locations

Identified by its extreme hardness (scratches glass), waxy texture, and sharp curved edges when broken. Commonly found in nodules within limestone or as river pebbles.