sedimentary
Chert
Microcrystalline silica (SiO2)
Hardness: 7 on Mohs scale; Color: Sage green, grey, or tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Sage green, grey, or tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Sage green, grey, or tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed from the accumulation of siliceous remains of marine organisms or via chemical precipitation in sedimentary environments. Common in marine limestone formations.
Uses & applications
Used historically for stone tools and weapons due to its sharp edges; industrially used as an abrasive or in road construction; popular for lapidary work.
Geological facts
Also known as flint when found in chalk. It was one of the first materials used by prehistoric humans to create fire and sharp arrowheads because it produces sparks and predictable fractures.
Field identification & locations
Identify by its ability to scratch glass and its shell-like (conchoidal) fracture patterns. Frequently found in riverbeds or as nodules within limestone outcrops.
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