sedimentary

Chert (Nodule)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Tan to light brown; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Tan to light brown
Luster: Dull to waxy

Identified June 29, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan to light brown; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds. Most common in Paleozoic to Cenozoic strata.

Uses & applications

Historically used for stone tools (arrowheads/scrapers) due to sharp edges; currently used for landscaping, road ballast, and as a raw material for silicon in some industries.

Geological facts

Chert is so hard it can scratch steel. When struck against steel, it can produce sparks, leading to its historical use as a fire-starter. It is extremely resistant to chemical weathering.

Field identification & locations

Identify in the field by its waxy texture and tendency to break along curved, shell-like (conchoidal) surfaces. Often found as rounded nodules or layers within softer limestone cliffs or in creek beds.