sedimentary

Chert (Smooth River Stone)

Microcrystalline or cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Gray with yellowish-brown iron staining; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Gray with yellowish-brown iron staining
Luster: Waxy to vitreous

Identified July 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation from silica-rich fluids within sedimentary rock layers. This specimen has been smoothed by fluvial (river) erosion over many years.

Uses & applications

Historically used for stone tools/arrowheads due to its sharp edges when broken. Today used in decorative landscaping, aquarium gravel, and as a material for lapidary tumbling.

Geological facts

Chert is extremely durable and chemically stable, which is why it often survives as a smooth pebble in riverbeds long after other rocks have eroded away. Varieties include flint, jasper, and agate.

Field identification & locations

Identify in the field by its waxy appearance, extreme hardness (it will scratch glass), and conchoidal (shell-like) fracture patterns. It is found globally in sedimentary basins and riverbeds.