sedimentary
Chert (Flint)
Chert (SiO2)
AI-generated identification · may be incorrectHardness: 7 Mohs; Color: Black, grey, or brown; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 Mohs
- Color
- Black, grey, or brown
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 Mohs; Color: Black, grey, or brown; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed as nodules or beds in sedimentary rocks through the accumulation of silica-rich organic remains or chemical precipitation from groundwater. Most common in Carboniferous or Cretaceous limestone formations.
Uses & applications
Historically used for stone tools and weapons; currently used for road surfacing, as grinding media, and for starting fires (flint and steel).
Geological facts
Commonly known as ‘flint’ when found in chalk or limestone; it was the primary material for prehistoric hand axes due to its ability to hold a sharp edge.
Field identification & locations
Identify by its waxy luster, extreme hardness (scratches glass), and characteristic shell-like (conchoidal) fractures. Found worldwide in limestone districts.
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Sandstone or Siltstone
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Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)
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