sedimentary
Chert (Yellow Jasper variant)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Ocher, tan, brown; Luster: Dull to waxy; Structure: Cryptocrystalline/Amorphous appearance; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Ocher, tan, brown
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Ocher, tan, brown; Luster: Dull to waxy; Structure: Cryptocrystalline/Amorphous appearance; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed via the accumulation of silica-rich microfossils or chemical precipitation from hydrothermal fluids in sedimentary basins. The yellow-brown hue comes from goethite or iron oxide inclusions.
Uses & applications
Historically used for stone tools (knapping); currently used for decorative pebbles, jewelry cabochons, and as a durable material in landscaping.
Geological facts
Commonly known as 'Jasper' when opaque and colored. It has been used by humans for hundreds of thousands of years to create sharp-edged tools due to its glass-like fracturing pattern.
Field identification & locations
Identify by its smooth, waxy texture and inability to be scratched by a steel knife. It often occurs as nodules in limestone or as smooth, water-worn river cobbles.
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Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
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Shale or Slaty Mudstone
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Sandstone
Arenite (primarily SiO2)
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