sedimentary
Chert (Flint) Nodule
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Tan, beige, brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Tan, beige, brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Tan, beige, brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the replacement of limestone/carbonate material by silica-rich fluids or the accumulation of siliceous organisms in a marine environment. Common in sedimentary basins worldwide.
Uses & applications
Historically used for stone tools and starting fires; currently used in construction aggregate, road surfacing, and as a landscaping stone.
Geological facts
Because it breaks with a conchoidal (shell-like) fracture, it creates edges sharper than a surgeon's scalpel, which is why it was the primary material for prehistoric arrowheads and tools.
Field identification & locations
Identify in the field by its hardness (it will scratch glass and steel), waxy feel, and smooth, curved fracture surfaces. Often found embedded in limestone or as loose river rocks.
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