sedimentary
Chert (Flint) / Silicified Limestone
Microcrystalline Quartz (SiO2)
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
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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.
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