sedimentary
Chert (varietal: Flint/River Pebble)
Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs scale; Color: Dull olive green to grayish-tan; Luster: Waxy to vitreous; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Dull olive green to grayish-tan
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 Mohs scale; Color: Dull olive green to grayish-tan; Luster: Waxy to vitreous; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through biochemical precipitation of silica from sea life (like radiolaria or diatoms) or chemical replacement of carbonate materials. This specimen appears water-worn, smoothed by fluvial or coastal action over millions of years.
Uses & applications
Used historically for stone tools (knapping) due to its sharp edges; currently used for road ballast, hardscape landscaping, and sometimes tumbled for jewelry or craft use.
Geological facts
Chert and flint were among the first materials used by early humans for tools and starting fires (striking against steel). Smaller pebbles like this are often part of widespread 'river gravel' deposits.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, waxy texture. Frequently found in riverbeds, glacial tills, and limestone-heavy coastal regions worldwide.
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