sedimentary
Chert (Flint)
Chert (Microcrystalline Quartz, SiO2)
Hardness: 7 on Mohs scale; Color: Gray, brown, or tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Gray, brown, or tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, brown, or tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments. It is often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for making stone tools (arrowheads/knives) due to its sharp conchoidal fracture. Today used in road construction, as semi-precious gemstones when colorful (Jasper), or as fire-starters.
Geological facts
Chert was one of the most important materials for prehistoric humans. Because it sparks when struck against steel, it was the primary mechanism for 'flintlock' firearms.
Field identification & locations
Identify by its waxy texture, extreme hardness (it will scratch glass), and the way it breaks into smooth, curved 'shell-like' surfaces. Commonly found in riverbeds or eroding out of limestone cliffs.
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