sedimentary

Chert (Iron-stained)

Chert (Silicon Dioxide, SiO2)

Hardness: 7 (Mohs scale); Color: Yellowish-brown to rust-orange due to iron oxide staining; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 - 2.65.

Hardness: 7 (Mohs scale)
Color: Yellowish-brown to rust-orange due to iron oxide staining
Luster: Dull to waxy

Identified April 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater. This specimen shows significant oxidation/weathering from iron-rich environments.

Uses & applications

Used historically for stone tools (arrowheads/scrapers), as road ballast, in glass manufacturing, and sometimes as landscaping stone or for lapidary tumbling.

Geological facts

Chert is so hard it can strike sparks against steel, a property that led to its sister-rock, flint, being used in early firearms. The yellow-brown color specifically often indicates the presence of Limonite or Goethite.

Field identification & locations

Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like 'conchoidal' fractures. Often found as nodules in limestone or as stream-worn cobbles.

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