sedimentary
Flint (Chert Nodules)
SiO2 (Cryptocrystalline Quartz)
Hardness: 7 on Mohs scale. Color: Dark gray to black interior with a light-colored whitish or tan weathered outer chalky cortex. Luster: Waxy to vitreous. Fracture: Conchoidal with sharp edges. Structure: Microcrystalline/cryptocrystalline aggregate.
- Hardness
- 7 on Mohs scale
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on Mohs scale. Color: Dark gray to black interior with a light-colored whitish or tan weathered outer chalky cortex. Luster: Waxy to vitreous. Fracture: Conchoidal with sharp edges. Structure: Microcrystalline/cryptocrystalline aggregate.
Formation & geological history
Formed as diagenetic nodules in sedimentary environments, specifically within chalk or limestone formations where biogenic silica (from radiolarians, sponge spicules, etc.) redeposited into concentrated siliceous concretions.
Uses & applications
Historically used for flintknapping (prehistoric tools, arrowheads, axes) and flintlock firearms. Today used as an abrasive, decorative stone, construction aggregate, and by outdoor enthusiasts for spark-striking fire starters.
Geological facts
Flint was one of the earliest materials mined and traded by early humans in the Stone Age due to its ability to split with predictable, glass-like sharp edges. The chalky white exterior around the specimen is a weathered patina or cortex formed by exposure and weathering.
Field identification & locations
Identified in the field by its distinct smooth gray/black translucent glass-like core wrapped in a rougher, chalky exterior ring, along with its sharp conchoidal fracture when broken. Frequently found along chalk cliffs, beaches, and limestone quarries in the UK, Western Europe, and North America.
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