sedimentary
Chert / Flint
Chert (Microcrystalline Quartz, SiO2)
Hardness: 7 on Mohs scale; Color: Grey, brown, white; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Grey, brown, white
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Grey, brown, white; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed as nodules in sedimentary rocks like limestone or chalk through the precipitation of silica from groundwater or organic remains (radiolarians/diatoms) during the Paleozoic to Cenozoic eras.
Uses & applications
Historically used for stone tools and fire-starting; currently used in construction aggregate, road surfacing, and as decorative landscape stones.
Geological facts
Flint was the primary material for prehistoric technology for over 2 million years. It creates sharp edges when struck and sparks when hit against steel.
Field identification & locations
Identify by its 'waxy' appearance and smooth, shell-like (conchoidal) curved breaks. Found globally in chalk and limestone beds or as rounded pebbles in stream beds/beaches.
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