sedimentary
Chert (often called Flint)
Chert (SiO2)
Hardness: 7.0 (Mohs scale), Color: Varying shades of gray, brown, and black with tan weathering rind, Luster: Waxy to vitreous, Crystal Structure: Microcrystalline/Cryptocrystalline, Cleavage: None (Conchoidal fracture), Specific Gravity: 2.65
- Hardness
- 7
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Physical properties
Hardness: 7.0 (Mohs scale), Color: Varying shades of gray, brown, and black with tan weathering rind, Luster: Waxy to vitreous, Crystal Structure: Microcrystalline/Cryptocrystalline, Cleavage: None (Conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Forms through the accumulation of silica-rich organic remains or chemical precipitation from fluids, often within limestone or shale beds. Common in formations ranging from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools and weapons due to sharp edges; currently used as aggregate, decorative stone, and occasionally in jewelry (as jasper or agate variants).
Geological facts
Chert was one of the most important raw materials for early humans; it produces sparks when struck against steel, which made it vital for fire-starting and flintlock firearms.
Field identification & locations
Identify by its characteristic conchoidal (shell-like) fracture edges, waxy feel, and ability to scratch glass. Widely found in sedimentary basins and riverbeds globally.
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