sedimentary
Chert (Yellow Jasper)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 6.5-7 (Mohs scale); Color: Ocher yellow to brownish; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 6
- Color
- Ocher yellow to brownish
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Ocher yellow to brownish; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich fluids or biological remains (like radiolarians) in sedimentary basins, often replacing limestone or forming as nodules. Can be hundreds of millions of years old.
Uses & applications
Historically used for stone tools and arrowheads due to sharp fracturing; currently used in lapidary work, jewelry, and as decorative river stone.
Geological facts
This specimen is often called 'Yellow Jasper' when it is opaque and colored by iron oxides (limonite/goethite). It is one of the most durable rocks found in river beds.
Field identification & locations
Identify by its 'waxy' texture and conchoidal (shell-like) fracture pattern. It will easily scratch glass. Commonly found in river gravels, desert pavements, and limestone outcrops.
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