sedimentary

Chert (Banded)

Cryptocrystalline Silica (SiO2)

Hardness: 7 Mohs scale; Color: Red, brown, and gray banding; Luster: Waxy to dull; Crystal structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 Mohs scale
Color: Red, brown, and gray banding
Luster: Waxy to dull

Identified July 9, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Red, brown, and gray banding; Luster: Waxy to dull; Crystal structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed in marine environments through the precipitation of silica-rich fluids or the accumulation of siliceous organisms (like radiolaria or diatoms) within sedimentary beds. The banding results from varying mineral impurities like iron oxide during deposition.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges. Today used in construction aggregate, landscaping, and as a lapidary material for polishing.

Geological facts

This specimen appears to be a 'flake' or fragment, possibly related to lithic reduction (tool making). Chert is so durable it often survives long after the surrounding limestone or chalk has weathered away.

Field identification & locations

Identified by its extreme hardness (scratches glass), waxy texture, and smooth, curved (conchoidal) fracture surfaces. Commonly found in stream beds or eroded out of limestone outcrops.