sedimentary
Chert (variations include Flint/Jasper)
Chert (SiO2)
Hardness: 6.5-7. Color: Gray, brown, rusty orange-red. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (has conchoidal fracture). Specific Gravity: 2.5-2.8.
- Hardness
- 6
- Color
- Gray, brown, rusty orange-red
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7. Color: Gray, brown, rusty orange-red. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (has conchoidal fracture). Specific Gravity: 2.5-2.8.
Formation & geological history
Formed from the accumulation of microscopic silica-rich organisms or chemical precipitation of silica in marine environments. Often found as nodules within limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads). Modern uses include road surfacing, jewelry (when colorful), and industrial abrasives.
Geological facts
Because it breaks with a sharp edge, it was the primary material for prehistoric survival. It is so hard that it can strike sparks from steel, hence its related name 'flint'.
Field identification & locations
Identify by its 'waxy' texture and shell-like (conchoidal) breakage patterns. Look for it in riverbeds or eroding limestone cliffs. It is resistant to weathering and often appears as rounded river cobbles like this one.
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