sedimentary
Chert (Flint)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Gray, tan, or brown; Luster: Waxy to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Gray, tan, or brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, tan, or brown; Luster: Waxy to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from groundwater within sedimentary beds. Most common in limestone or chalk deposits.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; modern uses include road surfacing, jewelry (as jasper), and flint-starting tools.
Geological facts
Chert has been used by humans for hundreds of thousands of years for tool-making because it breaks into predictably sharp, glass-like edges. It is extremely chemically stable and resistant to weathering.
Field identification & locations
Identify in the field by its waxy texture, inability to be scratched by steel, and unique conchoidal (shell-like) fracture patterns. Frequently found in riverbeds or eroding out of limestone cliffs.
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