sedimentary

Chert (likely flint-bearing chert)

Microcrystalline quartz, SiO₂ (chalcedony/quartz aggregate)

AI-generated identification · may be incorrect

Gray to blue-gray, opaque, waxy to dull luster, very fine-grained with conchoidal fracture and sharp edges; Mohs hardness about 7, no cleavage, specific gravity about 2.6. The visible pale patches and rough weathered cortex are consistent with natural chert nodules.

Identified September 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces carbonate sediments or when biogenic silica accumulates and lithifies, commonly in limestone or chalk. It can range from Precambrian to Cenozoic in age; the exact age and locality cannot be determined from the image.

Uses & applications

Used historically for tools, fire-starting, and weapons; crushed chert is used as aggregate and road material. Attractive polished pieces are collected, though this specimen appears primarily geological rather than gem quality.

Geological facts

Chert is chemically similar to quartz but lacks visible crystals because its silica is cryptocrystalline. Flint is a dark, particularly dense variety of chert, often associated with chalk deposits.

Field identification & locations

Identify by its glassy or waxy surface, conchoidal fracture, lack of visible grains, and ability to scratch ordinary glass. Common in limestone and chalk regions worldwide; avoid confusing it with slag or fine-grained volcanic rock.