sedimentary
Chert (Flint)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, brown, or tan with a waxy/dull luster; Crystal Structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Gray, brown, or tan with a waxy/dull luster
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, brown, or tan with a waxy/dull luster; Crystal Structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the precipitation of silica from water or the accumulation of siliceous biological remains (like diatoms or radiolarians) in deep-sea environments. Often found as nodules within limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads/knives) due to sharp edges; currently used for road surfacing, as a component in glassmaking, and for fire-starting striking kits.
Geological facts
Chert was one of the most vital materials for early humans; its ability to break into 'conchoidal' (shell-like) fractures creates edges sharper than a steel scalpel. The specimen in the image appears to have been worked or 'knapped', suggesting it may be a lithic flake or debitage from tool making.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), waxy texture, and sharp, curved fracture patterns. Common in sedimentary basins worldwide, particularly in areas with limestone outcroppings.
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