sedimentary

Banded Chert

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Gray, tan, brown, and black banding; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65

Hardness: 6
Color: Gray, tan, brown, and black banding
Luster: Waxy to dull

Identified June 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as an inorganic chemical precipitate or from the accumulation of siliceous biological remains (like radiolarians or diatoms) on the ocean floor. It is often found in prehistoric marine sedimentary sequences.

Uses & applications

Historically used for making stone tools (arrowheads/scrapers) due to conchoidal fracture; modernly used in landscaping, as a construction aggregate, or tumbled for lapidary collections.

Geological facts

Chert was one of the first materials used by early humans for fire-starting and weaponry because it breaks into sharp edges. Banded varieties like this one often indicate fluctuations in water chemistry during deposition.

Field identification & locations

Identify by its extreme hardness (will scratch glass), waxy luster when broken, and lack of visible grains. Commonly found in limestone or chalk beds and along riverbeds or beaches where it has been tumbled smooth.