sedimentary
Chert / Flint
Silicon Dioxide (SiO2)
AI-generated identification · may be incorrectHardness: 6.5-7 Mohs. Color: Gray, tan, white, or brown. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
- Hardness
- 6
- Color
- Gray, tan, white, or brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs. Color: Gray, tan, white, or brown. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
Formation & geological history
Formed by the precipitation of microcrystalline silica from water, often replacing organic material or occupying voids in limestone or chalk. Dates back to various geological periods from the Precambrian to present day.
Uses & applications
Used historically for stone tools and starting fires (flint). Currently used in road construction, landscape gravel, and occasionally as decorative stones.
Geological facts
Chert was one of the most important minerals for early humans because of its ability to break into sharp edges for arrowheads and scrapers. It is chemically identical to quartz but with a microscopic grain structure.
Field identification & locations
Identify by its waxy texture, extreme hardness (it will scratch glass), and shell-like (conchoidal) fractures. Found worldwide in riverbeds, glacial tills, and sedimentary outcrops.
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