sedimentary

Banded Chert

Silicon dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Gray, green, and black banding; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 6
Color: Gray, green, and black banding
Luster: Waxy to vitreous

Identified June 27, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Gray, green, and black banding; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & geological history

Formed from the accumulation of siliceous remains of microscopic marine organisms (like radiolarians or diatoms) or by chemical precipitation from silica-rich fluids in ocean basins.

Uses & applications

Historically used for making stone tools (arrowheads/scrapers); currently used for decorative stones, tumbling for jewelry, and as a component in construction aggregates.

Geological facts

Chert is one of the most durable sedimentary rocks. Similar specimens from the Precambrian era often contain some of the oldest microfossils on Earth.

Field identification & locations

Look for distinct, alternating color bands and a smooth, waxy feel. It will scratch glass and break with sharp, curved edges. Found worldwide in beach gravels, riverbeds, and limestone outcrops.