sedimentary

Chert (Nodule)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs); Color: Tan, brown, or buff; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 6
Color: Tan, brown, or buff
Luster: Waxy to dull

Identified April 7, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs); Color: Tan, brown, or buff; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed by the precipitation of silica within sedimentary layers, often replacing organic material or filling voids in limestone. This specimen appears to be a nodular chert typically found in Cretaceous or Jurassic limestone formations.

Uses & applications

Historically used for stone tools (arrowheads/scrapers) due to its sharp edges; modern uses include construction aggregate and occasionally as a tumbling stone for collectors.

Geological facts

Chert is so hard it can scratch steel and is famously known in its dark form as flint, which was essential for starting fires and making firearms in history.

Field identification & locations

Identify by its 'glassy' or conchoidal fracture patterns (curved breaks) and resistance to scratching by a steel blade. Found in sedimentary basins worldwide, often weathering out as rounded nodules.