sedimentary
Chert / Flint
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 7 on Mohs scale; Color: Tan, beige, or grey; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65.
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, or grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, or grey; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in marine or groundwater environments; often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools and starting fires; modern uses include aggregate in road construction, gemstone tumbling, and as flint in decorative landscaping.
Geological facts
Because it breaks with a conchoidal (shell-like) fracture, it produces edges sharper than a surgeon's scalpel, which made it the primary material for prehistoric arrowheads and knives.
Field identification & locations
Identify by its 'sharp' edges, waxy feel, and ability to scratch glass; commonly found in bridge embankments, gravel pits, and riverbeds throughout North America and Europe.
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