sedimentary
Chert (White Chert/Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: White to off-white; Luster: Waxy to dull; Structure: Cryptocrystalline; Fracture: Conchoidal; Specific Gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- White to off-white
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White to off-white; Luster: Waxy to dull; Structure: Cryptocrystalline; Fracture: Conchoidal; Specific Gravity: 2.6-2.7
Formation & geological history
Forms through the precipitation of silica from groundwater or the accumulation of siliceous skeletal remains (like diatoms or radiolaria) in marine environments. Often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges. Modern uses include road surfacing, decorative landscaping, and as a raw material for silicon production.
Geological facts
Chert is so hard it can easily scratch glass and steel. It was one of the most important minerals for early humans because of how it breaks into extremely sharp, predictable edges.
Field identification & locations
Identify in the field by its smooth, shell-like (conchoidal) fracture patterns and ability to spark when struck against steel. Found globally in sedimentary basins, particularly within carbonate rock layers.
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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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Clastic Sedimentary Rock Grain (SiO2 dominated)
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