sedimentary

Chert (Chert Nodule)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Gray, tan, brown with red iron staining; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Hardness: 6
Color: Gray, tan, brown with red iron staining
Luster: Waxy to dull

Identified May 31, 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 chemical precipitation within limestone or chalk beds. This specimen appears to be a nodule with a weathered outer cortex.

Uses & applications

Historically used for stone tools (arrowheads and scrapers) due to its sharp conchoidal fracture. Currently used in road construction, as decorative landscaping stone, and as a source of silica.

Geological facts

Chert is extremely durable and chemically stable, often surviving millions of years of erosion. Some varieties of chert, like flint, were the primary material for the first human industrial age.

Field identification & locations

Identify by its waxy texture, extreme hardness (it will scratch glass), and the way it breaks into smooth, curved shell-like surfaces. Often found in limestone outcrops or as rounded cobbles in riverbeds.