sedimentary
Chert (Chert Nodule)
Microcrystalline quartz (SiO2)
Hardness: 7 Mohs; Color: Grey, brown, white; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 Mohs
- Color
- Grey, brown, white
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs; Color: Grey, brown, white; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed by the accumulation and diagenesis of silica-rich organic remains or chemical precipitation within marine or land-based sedimentary layers like limestone or chalk. Many date from the Paleozoic or Mesozoic eras.
Uses & applications
Used historically for stone tools (flintknapping), as an industrial abrasive, or as decorative gravel. Higher-grade colorful varieties are used in lapidary work.
Geological facts
Flint is a variety of chert. Because of its conchoidal fracture, it was the primary material used by prehistoric humans to create sharp edges for arrowheads and scrapers.
Field identification & locations
Identify by its 'shell-like' curved fracture surfaces and its ability to scratch glass. Commonly found as nodules within limestone outcrops or along riverbeds and beaches.
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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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Clastic Sedimentary Rock Grain (SiO2 dominated)
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Shale or Slaty Mudstone
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Sandstone
Arenite (primarily SiO2)
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