sedimentary

Chert (Flint nodule)

Microcrystalline / Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness 7 on the Mohs scale; dark gray to smoky brownish core with a chalky white-to-tan exterior weathering rind (cortex); waxy to dull vitreous luster; cryptocrystalline microtexture; conchoidal fracture with sharp edges; specific gravity around 2.6 - 2.65.

Identified November 15, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as biochemical or diagenetic silica nodules within marine carbonate sediments (such as chalk or limestone) through the dissolution and reprecipitation of biogenic silica from siliceous sponges or radiolarians, predominantly during the Cretaceous Period.

Uses & applications

Historically knapped for prehistoric stone tools (arrowheads, blades, scrapers) and strike-a-light fire starters or flintlock mechanisms. Modernly used as decorative stone, aggregate, and for lapidary tumbling.

Geological facts

Flint was critical to human technological evolution in the Stone Age due to its predictable, extremely sharp conchoidal fracture. Striking flint against iron pyrite or steel produces sparks hot enough to ignite tinder, making it one of humanity's earliest fire-starting tools.

Field identification & locations

Look for a smooth, hard stone that cannot be scratched by a steel nail, often displaying a soft, weathered outer chalky crust (cortex) enclosing a dense, dark silica interior. Abundantly found in chalk downs, coastal beaches, and limestone beds across western Europe (e.g., UK, France) and North America.