sedimentary

Chert (Jasper/Flint variety)

Microcrystalline silicon dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Brown, tan, reddish-brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 7 (Mohs scale)
Color: Brown, tan, reddish-brown
Luster: Waxy to dull

Identified April 9, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Brown, tan, reddish-brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation in marine or groundwater environments. This specimen shows significant rounding typical of fluvial (river) transport, likely dating from various sedimentary eras.

Uses & applications

Historically used for stone tools and weapons due to its sharp conchoidal fracture. Today used as road gravel, in landscape gardening, and occasionally for lapidary work if it has high color patterns.

Geological facts

Chert is so hard it can scratch steel. When struck against steel, it can produce sparks, leading to its historical use in flintlock firearms and fire-starting kits.

Field identification & locations

Identify in the field by its waxy texture, lack of visible grains, and shell-like (conchoidal) curved breaks. It is very common in riverbeds and glacial tilt deposits.