sedimentary

Flint or chert fragment

Microcrystalline quartz (SiO₂), commonly with chalcedony and minor impurities

AI-generated identification · may be incorrect

Dark gray, fine-grained, dull to waxy luster, conchoidal fracture, and no visible crystals or cleavage; hardness about 6.5–7 Mohs, specific gravity roughly 2.6. The tan rim may be weathered cortex or iron-stained host material.

Identified September 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica-rich groundwater replaces or fills sediment, often in limestone or marine deposits; the specimen is likely Paleozoic–Mesozoic, though age cannot be determined from the image. Its sharp fracture and worked-looking edges may indicate natural breakage or human flaking.

Uses & applications

Used historically for arrowheads, scrapers, and fire-making tools; today it is mainly a teaching or collecting specimen and occasionally crushed for aggregate.

Geological facts

Flint is a dark variety of chert and can produce extremely sharp edges. Striking it against steel may create sparks, though this specimen’s apparent edge may be naturally fractured.

Field identification & locations

Identify by its homogeneous fine texture, waxy surface, and conchoidal fracture; it commonly occurs as nodules or beds in limestone and chalk. Exact identification would benefit from testing for a glassy fracture and examining the tan material.