sedimentary
Chert (specifically Flint or Common Opal)
Silicon Dioxide (SiO2)
Hardness: 6.5–7 on Mohs scale; Color: Cream, tan, and light brown; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7.
- Hardness
- 6
- Color
- Cream, tan, and light brown
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Cream, tan, and light brown; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through the chemical precipitation of silica in groundwater within sedimentary basins.
Uses & applications
Historical use for stone tools and weapons (arrowheads); currently used in road construction, stone age replicas, and lapidary work for jewelry.
Geological facts
Chert was one of the most important materials for early humans because its conchoidal fracture creates razor-sharp edges. It is chemically very stable and can survive millions of years on the Earth's surface.
Field identification & locations
Identify by its waxy texture, extreme hardness (it will scratch glass), and its characteristic shell-like (conchoidal) curved fracture patterns. Commonly found in limestone or chalk beds.
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