sedimentary
Chert / Flint Nodules
Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: tan, grey, cream, or white; Luster: waxy to dull; Structure: microcrystalline (no visible crystals); Cleavage: none, breaks with a conchoidal (shell-like) fracture.
- Hardness
- 6
- Color
- tan, grey, cream, or white
- Luster
- waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: tan, grey, cream, or white; Luster: waxy to dull; Structure: microcrystalline (no visible crystals); Cleavage: none, breaks with a conchoidal (shell-like) fracture.
Formation & geological history
Formed through the replacement of limestone or chalk by silica-rich fluids. Often occurs as nodules in sedimentary deposits, particularly from the Cretaceous period (approx. 66–145 million years ago).
Uses & applications
Historically used for stone tools (arrowheads). Modern uses include road aggregate, decorative landscaping stone, and as a component in ceramics.
Geological facts
Chert/Flint was one of the most important minerals to early humans because its conchoidal fracture allows it to be shaped into razor-sharp edges and it creates sparks when struck against steel.
Field identification & locations
Identify by its waxy texture, hardness (it will scratch glass), and the way it breaks into sharp, curved flakes. Commonly found in limestone outcrops, riverbeds, and chalk cliffs.
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