sedimentary
Chert (Siltstone / Flint)
SiO2 (Cryptocrystalline Quartz)
Hardness: 6.5-7 on Mohs scale. Color: Light grey-green with brownish-yellow iron oxide staining. Luster: Dull to waxy. Fracture: Conchoidal to sub-conchoidal. Grain size: Very fine-grained (microcrystalline).
- Hardness
- 6
- Color
- Light grey-green with brownish-yellow iron oxide staining
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Light grey-green with brownish-yellow iron oxide staining. Luster: Dull to waxy. Fracture: Conchoidal to sub-conchoidal. Grain size: Very fine-grained (microcrystalline).
Formation & geological history
Formed in marine or freshwater sedimentary environments through the precipitation of silica or accumulation of siliceous organism remains, followed by compaction and diagenesis.
Uses & applications
Historically used for knapping sharp tools, arrowheads, and spark-striking flintlock mechanisms. Modernly used as road aggregate or raw material in stone manufacturing.
Geological facts
Chert is known for its extreme hardness and sharp edges when broken, which made it one of the most vital raw materials for prehistoric toolmakers.
Field identification & locations
Identified by its fine grain, hardness (scratches steel), smooth waxy texture, and distinct sharp conchoidal fracture edges. Widely found in limestone and chalk formations globally.
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