sedimentary

Banded Chert

Silicon Dioxide (SiO2)

Hardness: 6.5-7.0 (Mohs). Color: Brown, tan, and gray bands. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None, conchoidal fracture. Specific gravity: 2.5-2.8.

Hardness: 6
Color: Brown, tan, and gray bands
Luster: Waxy to dull

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7.0 (Mohs). Color: Brown, tan, and gray bands. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None, conchoidal fracture. Specific gravity: 2.5-2.8.

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or by chemical precipitation in marine or freshwater environments. The banding represents changes in sediment composition over time.

Uses & applications

Historically used for stone tools due to its sharp edges when fractured. Modernly used as landscaping stones, in lapidary work for tumbled stones, and for geological study.

Geological facts

Banded chert is often associated with Banded Iron Formations (BIFs) which date back billions of years and represent the oxidation of the Earth's oceans. This specific piece appears to be a water-worn river pebble.

Field identification & locations

Identify by its extreme hardness (will scratch glass), smooth waxy feel, and fine-grained texture. Commonly found in riverbeds, glacial tills, and sedimentary basins worldwide.