sedimentary
Chert (Flint variety)
Silicon dioxide (SiO2)
Hardness: 7 Mohs scale; Color: Dark grey, smoky, or black with occasional white weathering rinds; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 Mohs scale
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs scale; Color: Dark grey, smoky, or black with occasional white weathering rinds; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed in marine environments as nodules and layers within limestone or chalk beds. It originates from the accumulation of microscopic silica-rich plankton remains that recrystallize into a dense mass.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) and fire-starting. Currently used in construction aggregate, road surfacing, and as a raw material for ceramics.
Geological facts
Flint was one of the most important resources for prehistoric humans because of its ability to produce a sharp edge and sparks when struck with steel or pyrite. It is essentially a variety of microcrystalline quartz.
Field identification & locations
Identify by its characteristic conchoidal fracture (curved, shell-like surfaces) and its ability to scratch glass. Commonly found along chalk cliffs, riverbeds, and in limestone quarries.
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