sedimentary
Chert (Yellow Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Pale yellow to mustard yellow with cream patches; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Pale yellow to mustard yellow with cream patches
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Pale yellow to mustard yellow with cream patches; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed via the precipitation of silica from groundwater or the accumulation of silica-rich organic remains in sedimentary basins. The yellow hue is typically caused by goethite or iron oxide inclusions.
Uses & applications
Commonly used for lapidary work, jewelry (beads/cabochons), and historically for stone tools due to its sharp fracture. It is also used in decorative landscaping.
Geological facts
Chert has been used by humans for millions of years to make arrowheads and scrapers. Yellow varieties are often categorized as 'Jasper' when they are opaque and colorful.
Field identification & locations
Identified by its extreme hardness (cannot be scratched by a steel knife) and waxy, smooth texture compared to the surrounding rock. Often found in riverbeds or limestone deposits throughout the Midwestern USA and coastal regions.
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