sedimentary
Flint with Chalk Cortex
Chert (Microcrystalline Quartz, SiO2)
AI-generated identification · may be incorrectHardness: 7 (Mohs scale), Color: Black to dark gray interior with a white/cream exterior, Luster: Waxy to vitreous, Structure: Cryptocrystalline, Fracture: Conchoidal
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Physical properties
Hardness: 7 (Mohs scale), Color: Black to dark gray interior with a white/cream exterior, Luster: Waxy to vitreous, Structure: Cryptocrystalline, Fracture: Conchoidal
Formation & geological history
Formed in marine sedimentary environments, specifically within Cretaceous chalk beds, by the replacement of calcium carbonate with silica from sponges or diatoms.
Uses & applications
Historically used for stone tools and starting fires; currently used for lapidary work, landscaping, and primitive technology demonstrations.
Geological facts
Flint nodules are often found with a white, porous outer layer called a cortex, which is a mixture of silica and calcium carbonate remnants from the surrounding chalk.
Field identification & locations
Look for a smooth, rounded or irregular nodule with a white 'skin'. If broken, it reveals a dark, glass-like interior. Commonly found on beaches near chalk cliffs like those in Dover, UK.
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