sedimentary

Chert (Jasper/Flint variety)

Microcrystalline silicon dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs scale; Color: Tan, brown, and grey mottled; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 7 Mohs scale
Color: Tan, brown, and grey mottled
Luster: Waxy to dull

Identified May 9, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Tan, brown, and grey mottled; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. This specific specimen appears to be a water-worn river cobble.

Uses & applications

Historically used for stone tools and weapons due to its sharp edges when broken. Currently used for landscaping, road aggregate, and as a lapidary material for polishing and jewelry.

Geological facts

Chert is so durable that it often survives long-distance transport in rivers and glacial deposits, which is why it is frequently found as rounded cobbles far from its original bedrock source.

Field identification & locations

Identify in the field by its hardness (it should scratch glass), waxy luster when wet, and distinctive conchoidal (shell-like) fracture patterns. Frequently found in riverbeds and gravel pits.