Yellow Chert (Jasper)

Physical Properties

Hardness: 6.5-7 Mohs; Color: Mustard yellow to tan; Luster: Waxy to dull; Crystal structure: Microcrystalline (Trigonal); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.58-2.91

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from groundwater in sedimentary basins. The yellow color is typically due to goethite or limonite inclusions.

Uses & Applications

Historically used for stone tools/arrowheads. Currently used in lapidary work, jewelry (cabochons), and as landscaping stone or gravel.

Geological Facts

Chert and Jasper are essentially the same mineral composition, with Jasper being the opaque variety. It is extremely durable and has been used by humans for hundreds of thousands of years for sharp-edged tools.

Field Identification & Locations

Identify by its waxy appearance and smooth, shell-like (conchoidal) fracture when broken. It is a common river rock found worldwide, especially in areas with ancient limestone or dolomite beds.

Identified on: 5/18/2026

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