sedimentary

Chert (Nodule)

Chert (Silicon Dioxide, SiO2)

Hardness: 7 on Mohs scale; Color: Tan, gray, or brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Hardness: 7 on Mohs scale
Color: Tan, gray, or brown
Luster: Waxy to dull

Identified June 14, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, gray, or brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation within limestone or chalk beds, often under marine conditions.

Uses & applications

Historically used for stone tools and weapons (flint-knapping); currently used in road construction, landscaping, and as a polishing abrasive.

Geological facts

Chert is extremely durable and can preserve microfossils. It has been used by humans for hundreds of thousands of years to create sharp-edged tools due to its predictable breaking pattern.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), smooth waxy feel, and curved 'clamshell' fracture patterns. Common in sedimentary basins worldwide.