sedimentary
Chert (specifically Flint or Jasper variant)
Microcrystalline quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Brown, reddish-brown, and gray with waxy luster. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Brown, reddish-brown, and gray with waxy luster
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Brown, reddish-brown, and gray with waxy luster. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the accumulation of siliceous remains of marine organisms or the chemical precipitation of silica in sedimentary basins. These specimens appear to be nodular chert typically found in limestone or chalk beds.
Uses & applications
Used historically for stone tools and weapons due to sharp edges; currently used in jewelry (lapidary), as abrasives, and for fire-starting in survival gear.
Geological facts
Chert was one of the first materials used by prehistoric humans to create tools. The sharp conchoidal edges are capable of being sharper than a surgical steel scalpel.
Field identification & locations
Identify by its waxy appearance, extreme hardness (it will scratch glass), and its characteristic shell-like (conchoidal) fracture pattern. Found globally in sedimentary rock outcroppings.
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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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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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