sedimentary

Chert (Nodule)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on the Mohs scale; Color: Brown, tan, and white; Luster: Dull to waxy; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on the Mohs scale
Color: Brown, tan, and white
Luster: Dull to waxy

Identified March 25, 2026More sedimentary →

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Physical properties

Hardness: 7 on the Mohs scale; Color: Brown, tan, and white; Luster: Dull to waxy; Crystal structure: Trigonal (microscopic); 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 in sedimentary environments. Often found as nodules in limestone or chalk beds. Ages range from Precambrian to Cenozoic.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges; used today as a decorative landscaping stone, in road construction as aggregate, and occasionally for lapidary work.

Geological facts

Chert is so hard it can scratch steel and glass. In historical contexts, it was a primary material for 'flint' strike-a-lights to create fire. The variety seen here with a white outer layer is often called 'chert with a cortex'.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture when broken and its extreme hardness. Often found in riverbeds or eroded from limestone cliffs. Collectors look for unique banding or fossil inclusions.