sedimentary

Flint

SiO2 (Cryptocrystalline Quartz / Chert)

Hardness: 7 on the Mohs scale. Color: Dark grey to black with a lighter weathering cortex. Luster: Waxy to vitreous on fresh conchoidal fracture surfaces. Crystal structure: Microcrystalline quartz (chalcedony). Cleavage: None, exhibits sharp conchoidal fracture. Specific gravity: 2.60 to 2.65.

Hardness: 7 on the Mohs scale
Color: Dark grey to black with a lighter weathering cortex
Luster: Waxy to vitreous on fresh conchoidal fracture surfaces

Identified August 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the chemical replacement of calcium carbonate in limestone or chalk by silica-rich solutions originating from siliceous skeletal remains of marine organisms (such as sponges or radiolarians) during deep burial diagenesis.

Uses & applications

Historically used extensively by ancient humans for making stone tools, arrowheads, and blades due to its predictable conchoidal fracture. Also used for starting fires with steel strikers and in historical construction.

Geological facts

Flint is completely compatible with the regional geology indicated (Vinnytsia region, Ukraine), where Cretaceous chalk and limestone deposits frequently contain abundant high-quality flint nodules.

Field identification & locations

Easily identified by its dark grey/black interior, lighter chalky outer cortex, waxy luster, and sharp conchoidal edges. Commonly found as nodules within chalk cliffs and limestone beds or eroded into river gravels.