sedimentary

Yellow Chert (Jasper)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Mustard yellow, tan, or ochre; Luster: Waxy to dull; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Mustard yellow, tan, or ochre
Luster: Waxy to dull

Identified July 17, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils or precipitation from silica-rich fluids in sedimentary basins. Often found in nodules within limestone or chalk beds, typically dating from the Paleozoic to Mesozoic eras.

Uses & applications

Used historically for stone tools and weapons due to its sharp edges when fractured. Today used for lapidary work, jewelry (cabochons), and as a decorative landscaping stone.

Geological facts

Yellow chert gets its distinctive color from iron oxide (limonite) impurities. In archaeological contexts, it is often referred to as 'flint' and was a primary material for knapping arrowhead points.

Field identification & locations

Identify in the field by its smooth, waxy surface and characteristic shell-like (conchoidal) fractures. It will easily scratch glass. Commonly found in riverbeds or eroded limestone outcrops.