sedimentary
Chert (Yellow Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Opaque yellow to mustard brown; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Opaque yellow to mustard brown
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Opaque yellow to mustard brown; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed from the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. The yellow color is caused by the presence of iron oxide (goethite) inclusions.
Uses & applications
Historically used for making stone tools due to its sharp edges; currently used for lapidary work, jewelry (cabochons), and as a decorative landscaping rock.
Geological facts
Chert and Jasper are essentially the same material, with the name 'Jasper' usually reserved for colorful, opaque varieties. It was one of the most important minerals for early humans to create fire-starting kits and arrowheads.
Field identification & locations
Identify by its smooth, waxy surface and shell-like (conchoidal) fracture pattern where broken. Commonly found in riverbeds, beaches, and sedimentary basins worldwide.
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