sedimentary
Chert (Arrowhead Debitage or Flake)
Microcrystalline silica (SiO2)
Hardness: 7 on the Mohs scale; Color: White to light grey with tan patches; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on the Mohs scale
- Color
- White to light grey with tan patches
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on the Mohs scale; Color: White to light grey with tan patches; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich microfossils or precipitation from pore fluids in limestone or chalk beds. Often found as nodules within sedimentary host rocks. This specific piece shows evidence of anthropogenic flaking.
Uses & applications
Historically used for making stone tools (lithics) like arrowheads and scrapers. Currently used in jewelry (as jasper/agate variants) and as a low-cost construction aggregate.
Geological facts
Chert has been used by humans for over 2 million years to create sharp-edged tools because of its predictable conchoidal fracture. Some varieties, like flint, were vital for starting fires in early history.
Field identification & locations
Identify by its 'shell-like' (conchoidal) fracture edges, extreme hardness (it will scratch glass), and waxy texture. It is commonly found in stream beds and areas with limestone outcrops. Collectors look for 'bulbs of percussion' which indicate human working.
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