sedimentary
Chert (Tan/Brown)
Silicon Dioxide (SiO2) - Cryptocrystalline Quartz
Hardness: 7 (Mohs scale); Color: Tan to light brown; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Tan to light brown
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan to light brown; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed via the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through the chemical replacement of limestone/dolostone. Can range from Precambrian to Holocene in age.
Uses & applications
Historically used for stone tools (arrowheads/scrapers) due to sharp edges; currently used for road aggregate, landscaping, and flint-knapping enthusiasts.
Geological facts
Chert and flint are essentially the same material; the term 'flint' is often reserved for specimens found within chalk or limestone. It is so hard it can scratch steel.
Field identification & locations
Identify by its 'shell-like' conchoidal fracture patterns and inability to be scratched by a steel knife. Commonly found in riverbeds or as nodules within limestone outcrops. Look for smooth, curved break surfaces.
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