sedimentary
Chert Nodules / Flint
Chert (Silicon Dioxide, SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, or brown with a lighter chalky rind; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, or brown with a lighter chalky rind
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, or brown with a lighter chalky rind; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed in sedimentary rocks (like limestone or chalk) through the replacement of calcium carbonate by silica-rich fluids. Often formed during the diagenesis process millions of years ago, frequently during the Cretaceous period.
Uses & applications
Historically used for stone tools (arrowheads, knives) due to sharp edges; currently used for road surfacing, grinding media, and occasionally as decorative landscaping stone.
Geological facts
Flint was essential to early human survival for both tool-making and fire-starting, as it produces sparks when struck against steel or iron pyrites.
Field identification & locations
Identified by its very smooth, glass-like 'conchoidal' fracture and a thin, white, chalky outer layer (cortex). It is commonly found in chalk hills or as pebbles on beaches and in riverbeds.
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