sedimentary

Chert (Agatized/Banded)

Chert (Microcrystalline Silicon Dioxide, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs scale; Color: Tan, cream, and gray with concentric banding; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 7 Mohs scale
Color: Tan, cream, and gray with concentric banding
Luster: Waxy to vitreous

Identified June 13, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) or chemical precipitation in sedimentary environments. The banding suggests rhythmic deposition or later silica replacement within a host rock over millions of years.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp edges; currently used for landscaping, aggregate, and as a semi-precious gemstone when polished.

Geological facts

Chert is so hard it can create sparks when struck against steel. It is one of the most common materials used by early humans for lithic technology.

Field identification & locations

Identify in the field by its hardness (will scratch glass), waxy feel, and smooth, curved (conchoidal) fracture surfaces. Commonly found in limestone or chalk beds as nodules or layers.