sedimentary

Dark flint or chert fragment

Microcrystalline quartz (SiO₂), likely flint/chert

AI-generated identification · may be incorrect

Hardness about 7 Mohs; dark gray to black, opaque, with a dull-to-waxy luster and irregular conchoidal fracture. The pale, rough rim may be weathered cortex or adhering host material; crystal grains are microscopic.

Identified August 8, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or fills pores in marine limestone, commonly during the Cretaceous or Jurassic, though chert occurs from Precambrian to recent rocks. The fragment appears naturally broken or possibly worked.

Uses & applications

Used historically for sharp tools, arrowheads, and fire-starting; today mainly collected or used decoratively. Quality lapidary material can be polished, but this small piece has limited commercial value.

Geological facts

Fresh flint fractures into razor-sharp edges and was essential to prehistoric toolmaking. “Flint” commonly refers to dark chert, especially from chalk formations.

Field identification & locations

Look for glassy conchoidal fracture, no visible grains, inability to scratch with a steel knife, and no reaction to dilute acid. Common in limestone, chalk, gravel deposits, and glacial till worldwide.