sedimentary

Yellow Chert

Sedimentary cryptocrystalline quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Yellowish-tan to mustard (due to iron oxides/limonite); Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Yellowish-tan to mustard (due to iron oxides/limonite)
Luster: Waxy to dull

Identified April 6, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation in marine environments. This specimen likely dates from the Paleozoic or Mesozoic eras.

Uses & applications

Historically used for stone tools/arrowheads due to its sharp edges when broken. Today used as road base, decorative landscaping gravel, and occasionally for lapidary tumbling.

Geological facts

Chert is so durable that it often survives as 'river rocks' long after the surrounding limestone or shale has eroded away. Yellow varieties are frequently called 'Jasper' if they are opaque and highly pigmented.

Field identification & locations

Identify by its waxy texture, extreme hardness (it will scratch glass), and conchoidal (shell-like) fracture patterns. Frequently found in stream beds or weathered out of carbonate rock formations.

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