sedimentary

Chert (Flint) / Silicified Limestone

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on the Mohs scale. Color: Gray, light brown, whitish to dark slate gray with dull to waxy luster. Cleavage: None (conchoidal to subconchoidal fracture). Specific Gravity: ~2.65.

Hardness: 6

Identified July 26, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on the Mohs scale. Color: Gray, light brown, whitish to dark slate gray with dull to waxy luster. Cleavage: None (conchoidal to subconchoidal fracture). Specific Gravity: ~2.65.

Formation & geological history

Formed biogenically or chemically in marine environments where microcrystalline silica replaces calcium carbonate in limestone or accumulates as siliceous ooze on the seafloor over millions of years.

Uses & applications

Historically used for making stone tools, arrowheads, and fire-starting flints. Modernly used as aggregate, landscaping stone, and occasionally as decorative material.

Geological facts

Chert has been utilized by humans since the Paleolithic era due to its ability to break with very sharp edges when struck (conchoidal fracture).

Field identification & locations

Identified by its high hardness (scratches glass easily), smooth or waxy texture, lack of reacting to acid (unlike limestone), and typical conchoidal fracture pattern. Extremely common worldwide in sedimentary rock formations.