sedimentary
Chert (often colloquially called Flint)
Microcrystalline or cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs); Color: Grey, tan, or brown with waxy luster; Crystal Structure: Hexagonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 (Mohs)
- Color
- Grey, tan, or brown with waxy luster
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Physical properties
Hardness: 7 (Mohs); Color: Grey, tan, or brown with waxy luster; Crystal Structure: Hexagonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Forms by the accumulation of siliceous remains (like diatoms or radiolarians) or through the chemical precipitation of silica in sedimentary environments such as limestone beds.
Uses & applications
Historically used for stone tools and weapons (flint knapping). Today used in road construction, as an abrasive, and occasionally for lapidary work.
Geological facts
Chert is so hard it can scratch steel and was used for centuries to create sparks for starting fires and firing muskets.
Field identification & locations
Identify by its 'waxy' appearance and sharp, curved (conchoidal) edges when broken. Commonly found in riverbeds or as nodules within limestone.
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