sedimentary

Chert / Yellow Jasper

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 on the Mohs scale. Color: Mustard yellow, yellowish-brown, tan. Luster: Waxy to dull. Fracture: Distinct conchoidal fracture with sharp edges. Structure: Microcrystalline/Cryptocrystalline.

Hardness: 6
Color: Mustard yellow, yellowish-brown, tan
Luster: Waxy to dull

Identified July 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via chemical sedimentation or silica replacement of limestone/chalk deposits, often enriched with iron oxides (goethite or hematite) giving it a rich yellowish-brown hue. Common in ancient marine and lacustrine deposits worldwide.

Uses & applications

Historically used for knapping stone tools, arrowheads, and fire-striking flints. Modern uses include cabochons for lapidary jewelry, landscaping stone, and rock tumbling collections.

Geological facts

Yellow chert is often called yellow jasper when opaque and fine-grained. Due to its cryptocrystalline nature, it fractures with smooth, curved surfaces creating razor-sharp edges, which made it indispensable to prehistoric humans.

Field identification & locations

Identified by its waxy luster, smooth conchoidal fracture, sharp edges, and inability to be scratched by steel. Widely found in river gravels, limestone quarries, and coastal pebble beaches.

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