sedimentary

Chert (with Fossiliferous Silicification)

Silicon Dioxide (SiO2) - Microcrystalline Quartz

Hardness: 7 (Mohs scale); Color: Tan/Cream base with brownish patterns; Luster: Waxy to dull; Structure: Cryptocrystalline (no visible grains); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Tan/Cream base with brownish patterns
Luster: Waxy to dull

Identified March 18, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the biochemical precipitation of silica-rich fluids within limestone or chalk beds. Often contains silicified remains of prehistoric organisms. Geological age typically spans from the Paleozoic to Cenozoic eras.

Uses & applications

Commonly used as construction aggregate, road base, and historically for stone tools due to its sharp conchoidal fracture. Some attractively patterned specimens are used in lapidary work or as pocket stones.

Geological facts

Chert is so hard it can spark when struck against steel. The patterns seen on this specific stone are likely ichnofossils (burrow marks) or partial silicified fossil remains that have been smoothed over time by water erosion.

Field identification & locations

Identify in the field by its superior hardness (cannot be scratched by a steel knife) and smooth, waxy texture. High concentrations are found in riverbeds, glacial tills, and coastal areas where limestone has weathered away.

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Brecciated Chert (Microcrystalline Silica)

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