sedimentary
Chert (Flint Nodules)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, white, and grey; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, white, and grey
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, white, and grey; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation 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 when broken. Today used as road surfacing, decorative gravel, and for start-striking (fire starting).
Geological facts
Chert is so hard it can scratch steel. When struck against steel, it produces sparks, which is why it was the primary material for flintlock firearms and early fire-making kits.
Field identification & locations
Identify in the field by its smooth, waxy texture and shell-like (conchoidal) breaks. It is very common in riverbeds and limestone outcrops globally. Look for a white 'cortex' or weathered outer layer.
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