sedimentary
Chert (specifically Flint or Gray Chert)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, or smoky blue-gray; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, or smoky blue-gray
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, or smoky blue-gray; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds. Most specimens date from the Paleozoic to Mesozoic eras.
Uses & applications
Abrasives, construction aggregate, historical tool-making (arrowheads, scrapers), and landscaping. Occasionally used in jewelry as cabochons.
Geological facts
This specimen appears to be a 'lithic flake' or a crude biface tool, showing signs of 'knapping' (deliberate human shaping). Chert was the primary material for stone-age technology due to its ability to produce razor-sharp edges.
Field identification & locations
Identify in the field by its smooth, waxy surface and conchoidal (shell-like) fractures. It is commonly found in limestone outcrops, riverbeds, and as nodules in chalk. Collectors look for bulbs of percussion or ripple marks indicating human modification.
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