sedimentary
Chert (Arrowhead Debitage or Spall)
Silicon Dioxide (SiO₂)
Hardness: 7 (Mohs scale); Color: Tan, beige, brown; Luster: Waxy to dull; Structure: Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Tan, beige, brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, beige, brown; Luster: Waxy to dull; Structure: Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in sedimentary environments. Often found as nodules within limestone or chalk beds.
Uses & applications
Historically used for stone tools (lithic technology). Modern uses include road surfacing, industrial abrasives, and as a component in glass manufacturing.
Geological facts
This specific piece shows ripples and sharp edges characteristic of 'conchoidal fracture,' indicating it may be 'debitage'—a byproduct flake created when a human ancestor was flintknapping a stone tool.
Field identification & locations
Identify in the field by its glass-like sharp edges, waxy feel, and lack of visible grains. It is often found in limestone outcrops or riverbeds. Collectors look for pieces with 'bulbs of percussion' or 'flake scars' which suggest human modification.
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