sedimentary

Chert (Septarian Nodules-like)

Silicon dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs scale); Color: Brown to dark grey with lighter infill; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Conchoidal fracture where chipped.

Hardness: 6
Color: Brown to dark grey with lighter infill
Luster: Waxy to dull

Identified July 13, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs scale); Color: Brown to dark grey with lighter infill; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Conchoidal fracture where chipped.

Formation & geological history

Formed as a chemical precipitate in sedimentary environments, often replacing organic materials or forming within carbonate rocks. The cracks (septaria) may result from dehydration of a gel-like core followed by mineral infiltration.

Uses & applications

Primarily of interest to collectors; historically used for stone tools due to sharp fracture edges; occasionally used in decorative landscaping.

Geological facts

Chert is so durable that it often survives as stream pebbles long after the surrounding limestone or shale has eroded away. The distinctive cracking pattern in this specimen resembles a miniature septarian concretion.

Field identification & locations

Identify by its hardness (surfaces won't be scratched by a steel knife) and fine-grained, smooth texture. Commonly found in riverbeds, gravel pits, and sedimentary outcrops.