sedimentary
Chert (Jasper/Flint variety)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, and reddish-brown due to iron oxidation; Lustre: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, and reddish-brown due to iron oxidation
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, and reddish-brown due to iron oxidation; Lustre: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed by the accumulation of silica-rich organic remains or chemical precipitation from groundwater. Often found as nodules or layers in limestone or chalk beds.
Uses & applications
Historically used for stone tools and weapons (arrowheads) due to sharp edges; currently used as road aggregate, architectural stone, and occasionally in lapidary work.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture produces extremely sharp edges, foundational for the Stone Age technology.
Field identification & locations
Identify in the field by its hardness (it scratches glass), waxy appearance on fresh breaks, and smooth, curved (conchoidal) fracture surfaces. Common in sedimentary basins.
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