sedimentary
Chert (Flint variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5–7 on Mohs scale; Color: light gray to white with tan weathering; Luster: waxy to dull; Structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 6
- Color
- light gray to white with tan weathering
- Luster
- waxy to dull
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: light gray to white with tan weathering; Luster: waxy to dull; Structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed by the precipitation of silica in sedimentary environments, often replacing carbonate material (limestone) or as nodules. Often originating from the accumulation of microscopic silica-walled organisms.
Uses & applications
Historically used for making stone tools (arrowheads, knives) due to its sharp edges; used in construction aggregates, road beds, and occasionally as an industrial grinding medium.
Geological facts
Chert and flint were essential to early human survival for tool making and starting fires. It is so tough that it was often used as ballast in historical ships.
Field identification & locations
Identify in the field by its characteristic smooth, bowl-shaped 'conchoidal' fractures and its ability to scratch glass or steel. Found globally in limestone and chalk deposits.
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