sedimentary

Chert (Yellow/Tan Variety)

Chert (SiO2)

Hardness: 6.5–7 (Mohs scale); Color: Tan/yellow/creamy; Luster: Dull to waxy; Crystal structure: Microcrystalline (Cryptocrystalline) hexagonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7.

Hardness: 6
Color: Tan/yellow/creamy
Luster: Dull to waxy

Identified March 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine or lacustrine environments. This specimen appears water-worn or tumbled, likely from a fluvial or coastal environment.

Uses & applications

Historically used for stone tools and weapons due to sharp conchoidal edges. Currently used in road construction as aggregate, in landscaping, and as a low-cost lapidary material for tumbling.

Geological facts

Chert is a chemical sedimentary rock and is often found as nodules within limestone or dolomite beds. It is practically indestructible and often outlasts the host rock due to its chemical stability and hardness.

Field identification & locations

Identify in the field by its superior hardness (scratches glass), smooth waxy feel when polished, and characteristic curved, shell-like (conchoidal) fractures. Found globally in riverbeds and limestone outcrops.