sedimentary

Chert Nodule

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale), Color: Brownish-tan with black/white banding, Luster: Waxy to dull, Crystal Structure: Trigonal (microcrystalline), Cleavage: Conchoidal fracture, Specific Gravity: 2.65

Identified July 15, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: Brownish-tan with black/white banding, Luster: Waxy to dull, Crystal Structure: Trigonal (microcrystalline), Cleavage: Conchoidal fracture, Specific Gravity: 2.65

Formation & geological history

Formed via the accumulation of silica-rich fluids within limestone or chalk beds. Silica often replaces organic material or fills voids during diagenesis, typically occurring in marine environments millions of years ago.

Uses & applications

Used historically for stone tools (arrowheads). Today used as decorative landscaping stone, in road construction, and as a collector's specimen.

Geological facts

Chert and flint are closely related; flint is often the name given to dark, high-quality nodules found in chalk. It breaks with sharp edges, which made it the primary material for prehistoric survival tools.

Field identification & locations

Identified by its waxy luster, extreme hardness (scratches glass), and unique concentric band pattern known as a 'bullseye' or nodular structure. Frequently found in limestone quarries or riverbeds.