sedimentary
Chert (variations include Flint)
Chert (Silicon Dioxide, SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, or grey; Luster: Dull, waxy, or vitreous; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, or grey
- Luster
- Dull, waxy, or vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, or grey; Luster: Dull, waxy, or vitreous; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation of silica in marine environments. Found in strata ranging from Precambrian to present day.
Uses & applications
Historically used for stone tools (knapping) and fire-starting. Modern uses include road surfacing, decorative gravel, and as a component in ceramics.
Geological facts
Chert is so hard it can scratch steel. High-quality dark varieties are often called 'Flint' and were the primary material used by prehistoric humans for arrowheads and axe heads due to their sharp conchoidal edges.
Field identification & locations
Identify in the field by its smooth, shell-like (conchoidal) fracture and its ability to scratch glass. It is commonly found as nodules in limestone or chalk beds. Collectors look for unique colors or instances containing micro-fossils.
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