sedimentary
Chert (often associated with Jasper)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs. Color: Gray, brown, rusty red (due to iron oxides), and white. Luster: Dull to waxy. Structure: Non-crystalline mass. Cleavage: None, exhibits conchoidal (shell-like) fracture.
- Hardness
- 6
- Color
- Gray, brown, rusty red (due to iron oxides), and white
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 Mohs. Color: Gray, brown, rusty red (due to iron oxides), and white. Luster: Dull to waxy. Structure: Non-crystalline mass. Cleavage: None, exhibits conchoidal (shell-like) fracture.
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from hydrothermal fluids in sedimentary basins. Often found as nodules or bedded layers.
Uses & applications
Historically used for stone tools (arrowheads). Modernly used in road construction, landscaping, and as a component in cement. High-quality colorful pieces are used as lapidary material.
Geological facts
Chert is so hard it can create sparks when struck against steel. It was one of the most important minerals for early human survival for making sharp blades.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel), waxy texture on fresh breaks, and smooth, curved fracture surfaces. Found worldwide in limestone and chalk deposits.
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Sandstone or Siltstone
Arenite (if sandstone)
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Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
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Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Shale or Slaty Mudstone
Argillaceous sedimentary rock
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Sandstone
Arenite (primarily SiO2)
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