sedimentary
Chert (often called Flint when dark or worked)
Cryptocrystalline silica (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Gray, tan, or brown with a waxy luster; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 6
- Color
- Gray, tan, or brown with a waxy luster
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Gray, tan, or brown with a waxy luster; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in marine environments. This specimen shows 'lithic reduction' or knapping, indicating it was shaped by humans.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; industrially used for road metal and in the production of glass and ceramics.
Geological facts
This particular piece is a 'lithic artifact,' likely a preform or a scraper. Chert's conchoidal fracture allows it to break into razor-sharp edges, making it the most important material for prehistoric tool-making.
Field identification & locations
Identify in the field by its waxy texture and characteristic curved, shell-like fracture scars. Common in limestone deposits. Collectors of artifacts look for 'flakes' or 'bulb of percussion' marks which prove human manipulation.
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