sedimentary

Chert (Banded)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale), Color: tan, grey, white with banding, Luster: dull to waxy, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.65

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: tan, grey, white with banding, Luster: dull to waxy, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or freshwater environments. The banding often represents seasonal or chemical fluctuations during deposition.

Uses & applications

Historically used for making stone tools (arrowheads). Today used in road construction, as an abrasive, and occasionally for lapidary work or polishing.

Geological facts

Chert is so hard it can strike sparks against steel. It is chemically identical to quartz but has a much finer, microscopic grain structure. Some cherts contain microscopic fossils of radiolaria or diatoms.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture and its ability to scratch glass. It is commonly found as nodules or layers within limestone or dolomite formations.