sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: tan, cream, brown; Luster: vitreous to waxy; Crystal Structure: Cryptocrystalline; Cleavage: none (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- tan, cream, brown
- Luster
- vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: tan, cream, brown; Luster: vitreous to waxy; Crystal Structure: Cryptocrystalline; Cleavage: none (conchoidal fracture).
Formation & geological history
Formed from the accumulation of silica-rich organic remains or chemical precipitation from groundwater within sedimentary rock layers, often limestone or chalk.
Uses & applications
Historically used for making stone tools (flintknapping); currently used in road construction, as decorative gravel, and occasionally for fire-starting.
Geological facts
Chert is so hard it can scratch steel and was one of the most important minerals for early humans to create sharp cutting tools like arrowheads and knives.
Field identification & locations
Identify in the field by its distinct waxy texture and shell-like (conchoidal) fractures. Found worldwide in nodules or bedded deposits within limestone.
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Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
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
Argillaceous sedimentary rock
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Sandstone
Arenite (primarily SiO2)
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