sedimentary
Chert (Flint)
Chert (Silicon Dioxide, SiO2)
Hardness: 7 (Mohs scale); Color: Tan, beige, grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Tan, beige, grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, beige, grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation from groundwaters in limestone or chalk beds. Most common in ancient marine sedimentary sequences.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; modernly used in road construction, as a flux in glassmaking, and for fire-starting strikers.
Geological facts
Chert is so hard it will scratch glass and even common steel. It has been used by humans for hundreds of thousands of years to create sharp-edged tools and weapons.
Field identification & locations
Identify by its waxy appearance, extreme hardness, and conchoidal (shell-like) fracture patterns. It is frequently found as nodules within limestone or as bedded deposits in riverbeds and coastal cliffs.
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