sedimentary
Chert Pebble (Yellow Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 6.5–7 on Mohs scale; Color: Opaque yellow to mustard brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7
- Hardness
- 6
- Color
- Opaque yellow to mustard brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Opaque yellow to mustard brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7
Formation & geological history
Formed through the accumulation of silica-rich microfossils or chemical precipitation in marine or groundwater environments. This specimen has been significantly water-worn and smoothed by alluvial (river) transport, likely over thousands to millions of years.
Uses & applications
Common varieties are used in decorative gravel and construction; high-quality colorful specimens (Jasper) are used in jewelry, lapidary arts, and as semi-precious gemstones.
Geological facts
Chert was one of the most important minerals to prehistoric humans because its conchoidal fracture produces extremely sharp edges, making it ideal for stone tools like arrowheads and scrapers.
Field identification & locations
Identify in the field by its waxy texture and inability to be scratched by a steel knife. It will also spark when struck against steel. Commonly found in riverbeds, glacial tills, and coastal beaches.
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