sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs; Color: Tan, brown, gray, and cream with waxy luster; Cleavage: None (conchoidal fracture); Crystal System: Trigonal (microcrystalline)
- Hardness
- 7 Mohs
- Color
- Tan, brown, gray, and cream with waxy luster
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Physical properties
Hardness: 7 Mohs; Color: Tan, brown, gray, and cream with waxy luster; Cleavage: None (conchoidal fracture); Crystal System: Trigonal (microcrystalline)
Formation & geological history
Formed by the accumulation of silica-rich fluids in sedimentary basins or by the replacement of calcium carbonate. Often found as nodules or layers in limestone and chalk beds.
Uses & applications
Historically used for stone tools/weapons; currently used as a decorative stone, in construction aggregate, and for starting fires (flint).
Geological facts
Chert has been used by humans for millions of years to make spear points and arrowheads because its conchoidal fracture produces extremely sharp edges.
Field identification & locations
Identify by its waxy luster, hardness (will scratch glass), and smooth, curved fracture surfaces. Found worldwide in sedimentary rock formations.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Sandstone
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