sedimentary
Chert (Flint Nodules)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Gray, black, tan, or brown; Luster: Waxy to dull; Crystal structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 6
- Color
- Gray, black, tan, or brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Gray, black, tan, or brown; Luster: Waxy to dull; Crystal structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation within limestone or chalk beds. Often Cretaceous in age.
Uses & applications
Historically used for stone tools and weapons (arrowheads); currently used in road construction, as a gemstone (jasper/agate varieties), and as flint for fire-starting.
Geological facts
Chert was one of the most important minerals for prehistoric humans due to its ability to be knapped into sharp edges. It is chemically identical to quartz but has a different microscopic structure.
Field identification & locations
Identify by its 'shell-like' conchoidal fracture patterns and inability to be scratched by a steel pocketknife. Common in limestone outcrops and riverbeds.
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