sedimentary
Chert (Yellow Jasper/Flint)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs); Color: Tan, yellow, ochre; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 6
- Color
- Tan, yellow, ochre
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Tan, yellow, ochre; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or by chemical precipitation from silica-rich groundwater. Often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools and starting fires; currently used for decorative landscaping, gravel, jewelry (as jasper), and as flint for flintlock mechanisms.
Geological facts
Chert breaks with a conchoidal fracture, creating sharp edges that made it the primary material for arrowheads and spear points throughout human history.
Field identification & locations
Identify by its waxy texture, extreme hardness (scratches glass), and the way it breaks into curved, shell-like chips. Found globally in sedimentary basins.
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