sedimentary

Banded Chert

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs scale; Color: Gray, tan, and brownish bands; Luster: Waxy to sub-vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.

Hardness: 7 Mohs scale
Color: Gray, tan, and brownish bands
Luster: Waxy to sub-vitreous

Identified June 27, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Gray, tan, and brownish bands; Luster: Waxy to sub-vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.

Formation & geological history

Formed primarily by the biochemical or chemical precipitation of silica in marine environments, often from the accumulation of siliceous organisms like diatoms or radiolarians, or via replacement of limestone.

Uses & applications

Used historically for stone tools due to sharp edges; currently used for decorative stones, road surfacing, or as a semi-precious gemstone in lapidary work.

Geological facts

Chert is essentially the same mineral as flint, jasper, and chalcedony. The banding represents changes in the depositional environment or oxygen levels during formation.

Field identification & locations

Identifiable by its hardness (scratches glass), smooth waxy feel, and distinctive conchoidal (shell-like) fracture patterns. Frequently found in limestone or chalk beds.