sedimentary
Chert (Smooth River Pebble)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Grayish-brown, tan, or olive-drab; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Grayish-brown, tan, or olive-drab
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Grayish-brown, tan, or olive-drab; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments. This specific specimen has been further shaped and polished by fluvial (river) erosion over thousands of years.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges; currently used for road surfacing, landscaping, and sometimes for lapidary work as tumbled stones.
Geological facts
Chert is so hard it can strike sparks from steel, which led to its historical use in flintlock firearms. The term 'flint' is often used interchangeably with dark-colored chert.
Field identification & locations
Identify in the field by its smooth, 'soapy' feel, extreme hardness (it will scratch glass), and its curved, shell-like (conchoidal) fracture pattern if broken. Commonly found in riverbeds, glacial tills, and limestone outcrops.
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