sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale. Color: Light grey to off-white with a pale chalky cortex exterior. Luster: Waxy to dull. Cleavage: None, exhibits sharp conchoidal fracture. Specific gravity: ~2.65.

Hardness: 7 on Mohs scale
Color: Light grey to off-white with a pale chalky cortex exterior
Luster: Waxy to dull

Identified July 23, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale. Color: Light grey to off-white with a pale chalky cortex exterior. Luster: Waxy to dull. Cleavage: None, exhibits sharp conchoidal fracture. Specific gravity: ~2.65.

Formation & geological history

Formed through the accumulation and chemical precipitation of microcrystalline quartz or silica-rich biogenic material (such as radiolarian or diatom ooze) within marine sedimentary deposits, often as nodules in limestone or chalk formations.

Uses & applications

Historically used for flintknapping to create prehistoric stone tools, arrowheads, and spark-striking tools. Modern usage includes decorative landscape stone and road construction aggregate.

Geological facts

Chert and flint were among the very first raw materials utilized by early humans due to their ability to produce extremely sharp edges when fractured.

Field identification & locations

Identified by its high hardness, smooth waxy appearance on freshly broken surfaces, and distinct curved conchoidal fractures. Commonly found in stream beds, gravel pits, and eroded limestone outcrops worldwide.