sedimentary
Chert (Pebble)
Chert (Microcrystalline Quartz, SiO2)
Hardness: 7 (Mohs); Color: Brown, grey, tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (Triagonal system); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 (Mohs)
- Color
- Brown, grey, tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs); Color: Brown, grey, tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (Triagonal system); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from groundwater within sedimentary layers. This specific specimen is a water-worn river pebble.
Uses & applications
Historically used for stone tools (arrowheads). Today used in road construction, landscaping, and occasionally as an abrasive or for lapidary tumbling.
Geological facts
Chert is so hard it can strike sparks from steel. Flint is a high-quality variety of chert. Because of its conchoidal fracture, it was the primary material for stone-age weaponry.
Field identification & locations
Identify by its 'waxy' texture, extreme hardness (cannot be scratched by a steel knife), and smooth, curved fracture surfaces. Commonly found in riverbeds, glacial till, and within limestone outcrops.
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