sedimentary
Chert (often called Jasper or Flint)
Microcrystalline Silica (SiO2)
Hardness: 7 (Mohs scale). Color: Brownish-red to earthy tan. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Brownish-red to earthy tan
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 (Mohs scale). Color: Brownish-red to earthy tan. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or the chemical replacement of limestone/dolomite. Often found in nodules or bedded layers.
Uses & applications
Used historically for stone tools and arrowheads due to its sharp edges; modern uses include road surfacing and as a gemstone when colorful (Jasper).
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture produces edges sharper than a steel scalpel. It is highly resistant to chemical weathering.
Field identification & locations
Identify by its hardness (will scratch glass), smooth waxy feel on broken surfaces, and lack of visible grains. Commonly found in stream beds or limestone outcrops.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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