sedimentary
Chert / Flint
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Grey, black, or brown; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
- Hardness
- 7 on Mohs scale
- Color
- Grey, black, or brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grey, black, or brown; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
Formation & geological history
Formed in sedimentary rocks where microcrystalline silica replaces organic material or precipitates from fluids, often in marine environments within limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads) and fire-starting; currently used as road aggregate, in glass manufacturing, and as a semi-precious gemstone when colorful (Jasper).
Geological facts
Flint is a variety of chert that was the first 'utility' mineral for humans, used to create fire and sharp blades during the Stone Age due to its ability to fracture into razor-sharp edges.
Field identification & locations
Identify by its waxy appearance and conchoidal (curved, glass-like) fracture patterns. It is extremely hard and will scratch glass easily.
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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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