sedimentary
Chert (Flint)
Silicon dioxide (SiO2)
Hardness: 7 (Mohs); Color: Brown, gray, or tan; Luster: Waxy to vitreous; Structure: Microcrystalline/Cryptocrystalline; Breakage: Conchoidal fracture
- Hardness
- 7 (Mohs)
- Color
- Brown, gray, or tan
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 (Mohs); Color: Brown, gray, or tan; Luster: Waxy to vitreous; Structure: Microcrystalline/Cryptocrystalline; Breakage: Conchoidal fracture
Formation & geological history
Formed from the recrystallization of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in sedimentary environments like limestone or chalk beds.
Uses & applications
Used historically for stone tools and starting fires; currently used as road aggregate, architectural stone, and occasionally in jewelry as Jasper.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture creates extremely sharp edges for knives and arrowheads.
Field identification & locations
Identify by its waxy texture, inability to be scratched by steel, and curved seashell-like fractures. Frequently found in riverbeds or as nodules within limestone outcrops.
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