Yellow Chert or Jasper

Physical Properties

Hardness: 6.5–7 on Mohs scale. Color: Yellow, tan, and brownish with waxy luster. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6–2.7.

Formation & Geological History

Formed through the accumulation of silica-rich fluids in sedimentary environments or by the replacement of carbonate rocks. Often found in riverbeds or coastal deposits where it has been tumble-polished by water over millions of years.

Uses & Applications

Historically used for stone tools (arrowheads). Modern uses include jewelry (cabochons), river rock landscaping, and as a popular specimen for rock tumbling and collecting.

Geological Facts

Yellow chert gets its color from iron oxide inclusions (limonite). It is extremely durable and chemical-resistant, which is why it often survives as rounded pebbles in gravel pits long after other rocks have eroded.

Field Identification & Locations

Identify in the field by its smooth, waxy feel, conchoidal (shell-like) fracture patterns, and its ability to scratch glass. Found globally in ancient seabed deposits and gravel beds.

Identified on: 4/29/2026

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