sedimentary
Chert (Flint)
Chert (Cryptocrystalline Quartz, SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, and grey; Luster: Waxy to dull; Crystal structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, and grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, and grey; Luster: Waxy to dull; Crystal structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed by the precipitation of silica-rich fluids or from the accumulation of siliceous remains of organisms (like diatoms or radiolaria) in marine environments. Often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used in landscaping, as a flint-starter for fires, and sometimes in road construction aggregate.
Geological facts
Flint is a variety of chert. When struck against steel, it produces sparks, which led to its extensive use in flintlock firearms and early fire-starting tools. It is one of the most common materials used by early humans for tool-making.
Field identification & locations
Identified in the field by its waxy texture, smooth conchoidal (shell-like) fractures, and its ability to scratch glass. It is commonly found in riverbeds, glacial till, and coastal chalk deposits.
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