sedimentary
Chert (Flint)
Chert (Silicon Dioxide, SiO2)
Hardness: 7 on Mohs scale; Color: Grey, brown, yellowish, or tan with waxy/dull luster; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Grey, brown, yellowish, or tan with waxy/dull luster
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Physical properties
Hardness: 7 on Mohs scale; Color: Grey, brown, yellowish, or tan with waxy/dull luster; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds. Often Paleozoic to Mesozoic in age.
Uses & applications
Historically used for stone tools and weapons (arrowheads); currently used as road aggregate, in glass manufacturing, and as a starting material for sparking (fire-making).
Geological facts
Chert is so hard it can scratch steel. When struck against iron or steel, it produces sparks due to its hardness and friction, making it a primary tool for survivalist fire-starting.
Field identification & locations
Identify by its waxy appearance, extreme hardness, and 'shell-like' conchoidal fractures. Commonly found in stream beds or weathered out of carbonate rock outcrops globally. Collectors look for colorful variants like jasper or agate.
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