sedimentary
Chert (Chalcedony-rich sedimentary rock)
Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, off-white; Luster: Waxy to dull; Structure: Microcrystalline/Cryptocrystalline; Fracture: Conchoidal; Specific Gravity: 2.6
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, off-white
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, off-white; Luster: Waxy to dull; Structure: Microcrystalline/Cryptocrystalline; Fracture: Conchoidal; Specific Gravity: 2.6
Formation & geological history
Formed primarily by the precipitation of silica in sedimentary environments, often within limestone or marl. It can originate from biological remains like diatom or radiolarian tests or through chemical replacement processes.
Uses & applications
Used historically for tool-making (arrowheads, scrapers) due to its sharp edges; used today as a construction aggregate and as a specimen for lapidary collectors.
Geological facts
Chert has been used by humans for hundreds of thousands of years to create fire (flint is a variety of chert) and sharp-edged tools. It is incredibly durable and resists chemical weathering.
Field identification & locations
Identify in the field by its distinct waxy appearance, extreme hardness (it will scratch glass/steel), and conchoidal (shell-like) fracture patterns. Found worldwide in sedimentary basins.
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Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
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Clastic Sedimentary Rock Grain (SiO2 dominated)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Shale or Slaty Mudstone
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Sandstone
Arenite (primarily SiO2)
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