sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale. Color: Grey, tan, off-white, and dark brownish-grey. Luster: Dull to waxy. Fracture: Conchoidal to sub-conchoidal. Microcrystalline structure. Specific gravity: 2.5-2.8.

Hardness: 7 on Mohs scale
Color: Grey, tan, off-white, and dark brownish-grey
Luster: Dull to waxy

Identified July 23, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale. Color: Grey, tan, off-white, and dark brownish-grey. Luster: Dull to waxy. Fracture: Conchoidal to sub-conchoidal. Microcrystalline structure. Specific gravity: 2.5-2.8.

Formation & geological history

Forms primarily in marine environments where silica-rich fluids replace calcium carbonate in limestone or chalk, or from the accumulation of siliceous organism remains (diatoms, radiolarians) on the seafloor over millions of years.

Uses & applications

Historically used for making stone tools, arrowheads, and spark-striking flintlocks. Modern uses include construction aggregate, road base, landscaping, and lapidary tumbling.

Geological facts

Chert and flint are composed of microscopic quartz crystals that break with extremely sharp edges, which made them essential toolmaking materials for early humans throughout prehistoric times.

Field identification & locations

Can be identified by its smooth, waxy feel, hardness (scratches glass), and distinctive sharp conchoidal fracture edges. Widely found in chalk and limestone formations, river beds, and coastal gravels worldwide.