sedimentary

Yellow Chert (Jasper/Flint variety)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Yellow-ochre due to iron oxide (limonite) inclusions; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.

Hardness: 6
Color: Yellow-ochre due to iron oxide (limonite) inclusions
Luster: Waxy to dull

Identified March 14, 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 or groundwater environments. This specimen appears water-worn, suggesting it was relocated by river or glacial action.

Uses & applications

Historically used for making stone tools (arrowheads/scrapers) due to its sharp conchoidal fracture. Modern uses include decorative landscaping, flint-knapping enthusiasts, and occasionally as minor gemstones (as Jasper).

Geological facts

Chert is so durable that it often remains behind after the surrounding limestone or chalk has eroded away. Yellow chert owes its specific color to the presence of goethite or limonite.

Field identification & locations

Identify in the field by its hardness (it will scratch glass) and its curved, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds, gravel pits, and as nodules in limestone outcrops.

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