sedimentary
Chert
Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Gray to brown; Luster: Waxy to dull; Fracture: Conchoidal; Structure: Microcrystalline; Specific Gravity: 2.6-2.7.
- Hardness
- 7 (Mohs scale)
- Color
- Gray to brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray to brown; Luster: Waxy to dull; Fracture: Conchoidal; Structure: Microcrystalline; Specific Gravity: 2.6-2.7.
Formation & geological history
Formed by the precipitation of silica from aqueous solutions, often as nodules in limestone or chalk, or as bedded deposits from the accumulation of siliceous organic remains like diatoms or radiolarians.
Uses & applications
Used in ancient times for stone tools (knapping) due to its sharp edges; used today as road surfacing material and in jewelry as decorative stones.
Geological facts
Chert and its variety, flint, were among the most important materials for early humans to create spearheads and arrowheads. It can spark when struck against steel.
Field identification & locations
Identify by its smooth, waxy surface and shell-shaped (conchoidal) fractures. It is commonly found in sedimentary basins and limestone outcrops worldwide.
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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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