sedimentary

Chert (River Pebble)

Chert (Silica, SiO2)

Hardness: 7 on Mohs scale; Color: Gray, tan, or brown; Luster: Waxy to dull (though this specimen appears wet or polished); Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Gray, tan, or brown
Luster: Waxy to dull (though this specimen appears wet or polished)

Identified June 18, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms through the accumulation of siliceous remains of organisms (like diatoms or radiolaria) or by chemical precipitation. This specific piece is a water-worn pebble, likely shaped by river or coastal erosion.

Uses & applications

Historically used for making stone tools (arrowheads). Today used in landscaping, as road base, and as decorative river stones. High-quality varieties like flint are used in fire-starting kits.

Geological facts

Chert is so hard it can easily scratch glass. When struck against steel, it produces sparks, which is why the variety known as flint was essential for early firearms and survival.

Field identification & locations

Identify in the field by its smooth, waxy texture and shell-like (conchoidal) fracture pattern if broken. Found globally in riverbeds, gravel pits, and sedimentary basins.