sedimentary

Chert or flint nodule/fragment

Microcrystalline quartz (SiO₂), commonly with chalcedony

AI-generated identification · may be incorrect

Typically Mohs hardness 6.5–7, waxy to dull luster, opaque brown-to-black color, and conchoidal fracture without cleavage. The dark outer material surrounds a reddish-brown weathered or altered interior, possibly with iron-oxide staining.

Identified August 16, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces carbonate sediment or fills cavities in limestone and chalk, commonly during the Mesozoic or Cenozoic; exact age cannot be determined from the image.

Uses & applications

Used historically for sharp-edged tools and fire-starting, and today as a lapidary or decorative material; specimens of this quality generally have little commercial value.

Geological facts

Its curved fracture surfaces and very fine grain distinguish chert from coarse-grained rocks. The triangular shape appears naturally fractured or human-shaped, but the specimen is not identifiable as a specific variety with certainty from a photograph alone.

Field identification & locations

Look for a glassy or waxy surface, conchoidal breaks, lack of visible grains, and the ability to scratch ordinary glass. Common sources include limestone terrains, chalk deposits, river gravels, and former sea-floor sediments.