sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs scale; Color: Dark grey to black with brown patina; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 Mohs scale
- Color
- Dark grey to black with brown patina
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs scale; Color: Dark grey to black with brown patina; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formation occurs as nodules or beds in limestone or chalk through the replacement of calcium carbonate by silica-rich fluids. Often formed during the Cretaceous period or earlier.
Uses & applications
Used historically for stone tools (arrowheads, scrapers) due to sharp edges; currently used as a decorative stone, in construction aggregate, and as a striker for fire-starting.
Geological facts
Flint is a variety of chert that occurs primarily in chalk and marly limestone. It was one of the most vital materials for early humans to create survival tools.
Field identification & locations
Identify by its conchoidal (shell-like) fracture patterns and ability to scratch glass. Commonly found in riverbeds, coastal chalk cliffs, and glacial till.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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