sedimentary

Banded Chert

Chert (Silicon Dioxide, SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Swirls of dark brown, black, and tan; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Swirls of dark brown, black, and tan
Luster: Waxy to vitreous

Identified July 17, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Swirls of dark brown, black, and tan; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation from groundwater within sedimentary layers. Over time, heat and pressure compress these layers into dense rock.

Uses & applications

Commonly used for lapidary work, decorative stones, and historically for stone tools like scrapers and arrowheads due to its sharp edges when broken.

Geological facts

This specimen is a water-worn or tumbled pebble showcasing distinct sedimentary banding. Chert is extremely durable and chemically resistant to weathering.

Field identification & locations

Identify it by its smooth, waxy feel, hardness (it will scratch glass), and the circular (conchoidal) patterns where it has chipped. Often found in riverbeds or coastal deposits.