sedimentary
Chert (Flint)
Chert (Silicon Dioxide, SiO2)
Hardness: 7 (Mohs scale); Color: Cream, tan, or white; Luster: Waxy to dull; Crystal structure: Microcrystalline (Trigonal); Cleavage: None (Conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Cream, tan, or white
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Cream, tan, or white; Luster: Waxy to dull; Crystal structure: Microcrystalline (Trigonal); Cleavage: None (Conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by the chemical replacement of limestone/chalk by silica-rich fluids. Commonly found in Paleozoic and Mesozoic sedimentary strata.
Uses & applications
Historically used for stone tools (arrowheads, knives) due to its sharp conchoidal fracture. Modern uses include abrasives, road surfacing, and as a component in glass and ceramics.
Geological facts
Chert has been one of the most important minerals for human survival, used for millions of years to create fires and sharp cutting tools. It is extremely chemically stable and resistant to weathering.
Field identification & locations
Identify by its waxy luster, hardness (it can scratch glass), and the curved (conchoidal) edges where it has broken. Look for nodules in limestone outcrops or as pebbles in stream beds.
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