sedimentary
Chert (Flint)
Chert (SiO2)
Hardness: 6.5-7. Color: Grey, black, or brown with a white weathered outer crust (cortex). Luster: Waxy to dull. Crystal Structure: Microcrystalline/Cryptocrystalline quartz. Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7. Color: Grey, black, or brown with a white weathered outer crust (cortex). Luster: Waxy to dull. Crystal Structure: Microcrystalline/Cryptocrystalline quartz. Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or by chemical precipitation in sedimentary environments. Common in limestone and chalk deposits.
Uses & applications
Historically used for making stone tools and starting fires (striking steel). Modernly used in construction aggregate and as a semi-precious stone in jewelry.
Geological facts
Flint is a variety of chert that occurs primarily in chalk or marly limestone. It was the primary material for the Stone Age technology due to its ability to flake into razor-sharp edges.
Field identification & locations
Identify by its very smooth, glass-like curved (conchoidal) fracture surfaces and its ability to scratch glass. Often found as nodules within limestone outcrops or as rounded pebbles in riverbeds.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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