sedimentary
Chert (Jasper/Flint var.)
Silicon Dioxide (SiO2)
Hardness: 7 Mohs scale; Color: Brownish-red to tan due to iron oxides; Luster: Waxy to dull; Crystal structure: Microcrystalline (Cryptocrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 Mohs scale
- Color
- Brownish-red to tan due to iron oxides
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs scale; Color: Brownish-red to tan due to iron oxides; Luster: Waxy to dull; Crystal structure: Microcrystalline (Cryptocrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from silica-rich fluids in limestone or chalk beds. Often Cretaceous to Paleozoic in age.
Uses & applications
Historically used for stone tools (knapping) due to sharp edges; currently used for road surfacing, jewelry (as Jasper), and landscaping.
Geological facts
Chert is so hard it can strike sparks against steel, which made it the primary material for flintlock firearms and ancient fire-starting kits.
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.
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