sedimentary

Gray chert or silicified limestone

Microcrystalline quartz (SiO₂), possibly with calcite (CaCO₃)

AI-generated identification · may be incorrect

Dense, dull gray-beige, opaque to slightly translucent material with a waxy luster and irregular conchoidal-looking fractures; quartz-rich portions are about Mohs 7, while calcitic areas are Mohs 3 and fizz in dilute acid. No obvious crystal faces are visible.

Identified August 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Likely formed when silica replaced or cemented carbonate sediment, producing chert or silicified limestone; the specimen’s geological age cannot be determined from the photograph. Such rocks commonly form in marine sedimentary sequences, nodules, or bedded limestone.

Uses & applications

Used locally as crushed aggregate, road stone, and historically for tools; attractive pieces may be collected, but this irregular specimen has little jewelry value.

Geological facts

Chert can preserve fossils or microscopic textures and commonly breaks with sharp, curved edges. A visible boundary between hard gray silica and pale, softer material would support partial silicification.

Field identification & locations

Common in limestone regions and sedimentary outcrops worldwide. Test hardness against glass and apply vinegar or dilute hydrochloric acid to separate quartz-rich chert from calcitic limestone; avoid destructive testing on valuable pieces.