sedimentary

Likely brecciated flint or chert

Microcrystalline quartz (SiO₂), possibly with calcite or silica-rich vein material

AI-generated identification · may be incorrect

Dark gray to black, waxy-to-dull luster with pale angular patches and a conchoidal-looking fracture; quartz hardness is about Mohs 7, with no cleavage and specific gravity near 2.6. The pale material may be calcite or weathered silica, but this cannot be confirmed from an image alone.

Identified August 23, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when dissolved silica replaces or accumulates within marine or lacustrine sediments, commonly during the Paleozoic–Cenozoic; brecciation and later veining produced the contrasting fragments. Exact age and identity require locality and testing.

Uses & applications

Used historically for sharp-edged tools and fire-starting; attractive pieces may be collected or used in lapidary work, though this specimen appears mainly of modest collector interest.

Geological facts

Fresh chert fractures into sharp conchoidal edges and may produce a glassy scratch; calcite-rich patches would fizz weakly in dilute hydrochloric acid, unlike quartz.

Field identification & locations

Common in limestone beds, river gravels, and glacial deposits worldwide; inspect fracture, test hardness against glass, and use acid only on a small pale area. Approximate value: $2–$20 for a small common specimen, potentially $25–$75 if locality-proven or unusually patterned.