sedimentary
Chert (Commonly known as Flint)
Silicon Dioxide (SiO2)
Hardness: 7 Mohs; Color: Tan, brown, or buff; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 Mohs
- Color
- Tan, brown, or buff
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs; Color: Tan, brown, or buff; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed by the precipitation of silica-rich fluids in sedimentary environments, often replacing carbonate rocks like limestone. It can occur as nodules or bedded deposits dating from various eras, including the Paleozoic.
Uses & applications
Historically used for making stone tools (arrowheads) and starting fires. Today used as road base, construction aggregate, and occasionally in jewelry as lapidary material.
Geological facts
Chert is so hard it will scratch steel. It breaks with sharp, razor-like edges, which made it the primary material for prehistoric humanity's tools and weapons for millennia.
Field identification & locations
Identify in the field by its waxy appearance and shell-like (conchoidal) fractures where it has been chipped. Commonly found in limestone outcrops or as rounded nodules in riverbeds.
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