sedimentary

Brown chert or flint pebble

Microcrystalline quartz (SiO₂), likely chert

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; opaque tan-brown surface with dull to waxy luster, very fine-grained texture, and conchoidal fracture. Its rounded shape indicates water abrasion; no visible cleavage or crystals.

Identified August 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica-rich microfossils or groundwater precipitate as cryptocrystalline quartz in sedimentary beds, commonly limestone or chalk. The pebble was later eroded and transported by water; its exact geological age cannot be determined from the image.

Uses & applications

Used historically for sharp tools and fire-starting, and today as a lapidary, landscaping, and decorative material. This ordinary rounded specimen has little jewelry value unless it displays unusual patterning or color.

Geological facts

Chert and flint are chemically similar; “flint” commonly refers to dark chert associated with chalk. A fresh broken edge should be glassy and sharply conchoidal.

Field identification & locations

Common in stream gravels, glacial deposits, and sedimentary regions worldwide; identify by its extreme hardness, silica-like fracture, and inability to scratch with a steel nail. Exact identification would require a fresh surface or testing.