sedimentary

Chert Pebble

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Tan, cream, and grey; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-2.8

Hardness: 7 (Mohs scale)
Color: Tan, cream, and grey
Luster: Waxy to dull

Identified July 19, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Tan, cream, and grey; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-2.8

Formation & geological history

Formed by the precipitation of silica from groundwater or the accumulation of siliceous skeletal remains of marine organisms. Usually found in nodules within limestone or as water-worn pebbles in stream beds.

Uses & applications

Historically used for making stone tools (arrowheads). Today used as construction aggregate, decorative landscaping stone, and occasionally for lapidary tumbling.

Geological facts

Chert is extremely durable and chemically stable, which is why it often survives as rounded pebbles in gravel pits and beaches long after the surrounding rock has weathered away.

Field identification & locations

Identify in the field by its hardness (it will scratch glass) and its smooth, waxy surface. Look for conchoidal (shell-like) fractures on broken edges.