sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Black, grey, or dark brown with white outer cortex; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture)
- Hardness
- 7 on Mohs scale
- Color
- Black, grey, or dark brown with white outer cortex
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Black, grey, or dark brown with white outer cortex; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture)
Formation & geological history
Formed by the precipitation of silica from groundwater or the accumulation of silica-rich microfossils (like radiolarians or diatoms) in marine sediments. Common in limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) and strike-a-lights for fire making. Modern uses include road aggregate and decorative landscaping stone.
Geological facts
Flint is a variety of chert that occurs in chalk or marly limestone. It was the primary material for the Stone Age technology due to its ability to hold a sharp edge when fractured.
Field identification & locations
Identify by its conchoidal (shell-like) fracture, ability to scratch glass, and waxy texture. Often found as nodules with a chalky white outer layer.
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