sedimentary
Chert / Flint
Silicon Dioxide (SiO2)
Hardness: 6.5-7 Mohs; Color: Tan, grey, or reddish-brown (often weathered); Luster: Waxy to dull; Structure: Cryptocrystalline/Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 6
- Color
- Tan, grey, or reddish-brown (often weathered)
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Tan, grey, or reddish-brown (often weathered); Luster: Waxy to dull; Structure: Cryptocrystalline/Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed by the accumulation of silica-rich microfossils (like radiolaria or diatoms) or by chemical precipitation from groundwater in sedimentary beds, often replacing limestone or chalk. Can be found in rocks from the Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp conchoidal edges; currently used as a grinding media in ball mills and in construction aggregate.
Geological facts
Flint is a variety of chert. When struck against steel, flint produces sparks, a property used for centuries to start fires and in flintlock firearms.
Field identification & locations
Identify by its 'shell-like' conchoidal fracture patterns on broken faces and its ability to scratch glass. Found globally in limestone formations and as smooth river/beach pebbles.
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