sedimentary
Chert (varieties include Flint and Jasper)
Silicon dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Grey, brown, or white; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Grey, brown, or white
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Grey, brown, or white; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from silica-rich fluids in sedimentary basins. Often found in limestone or chalk beds.
Uses & applications
Historically used for stone tools and starting fires (flint). Used today in road construction, and colorful varieties are used for lapidary work and jewelry.
Geological facts
Chert is so hard it can scratch glass and steel. It was one of the most vital resources for prehistoric humans because it fractures at sharp angles, creating cutting edges.
Field identification & locations
Identify by its waxy appearance and conchoidal (shell-like) fracture patterns. It is very hard and will not react to acid. Found globally, especially in areas with limestone outcrops.
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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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