sedimentary

Chert (Nodule)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Gray, brown, or tan with white weathering rinds; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Gray, brown, or tan with white weathering rinds
Luster: Waxy to dull

Identified May 28, 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 in marine environments, often as nodules within limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons due to sharp edges; currently used for road surfacing, as abrasive material, and occasionally in jewelry as Jasper.

Geological facts

Chert was one of the most vital resources for prehistoric humans because it fractures conchoidally, creating razor-sharp edges useful for arrowheads and scrapers.

Field identification & locations

Identify in the field by its hardness (it will scratch glass) and its smooth, shell-like fracture pattern. Common in riverbeds and limestone outcrops.