sedimentary
Chert / Flint
Silicon Dioxide (SiO2)
Hardness: 7 Mohs scale; Color: typically white, gray, or tan; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 Mohs scale
- Color
- typically white, gray, or tan
- Luster
- waxy to dull
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Physical properties
Hardness: 7 Mohs scale; Color: typically white, gray, or tan; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the precipitation of silica from seawater or in groundwater within carbonate rock. Often occurs as nodules or layers in limestone or chalk beds.
Uses & applications
Historically used for stone tools (knapping) and starting fires. Today used as a component in construction aggregate, road metal, and occasionally as a gemstone in jewelry.
Geological facts
Flint is a variety of chert. When struck against steel, it produces sparks due to the friction of the iron particles reacting with atmospheric oxygen.
Field identification & locations
Identify in the field by its distinct conchoidal (shell-like) fracture edges, waxy feel, and ability to scratch glass. Found globally in sedimentary basins.
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