sedimentary

Chert (Nodule)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale), Color: Dark brown to black with grayish-green patches, Luster: Waxy to dull, Crystal structure: Microcrystalline (Cryptocrystalline), Cleavage: None (Conchoidal fracture), Specific Gravity: 2.65

Identified May 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by the replacement of carbonate minerals in limestone or chalk beds. Often found in Phanerozoic sedimentary sequences.

Uses & applications

Historically used for making stone tools (flint knapping) due to its conchoidal fracture. Currently used in road construction, as an abrasive, and occasionally for lapidary work.

Geological facts

Chert is so hard that it can strike sparks from steel, which led to its famous use in flintlock firearms. It is chemically identical to quartz but has a different microscopic structure.

Field identification & locations

Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like fracture surfaces. Often found as nodules within limestone or as bedded layers.