sedimentary
Chert (Chalcedony/Flint)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Tan, brown, and grey mottled. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Tan, brown, and grey mottled
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Tan, brown, and grey mottled. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).
Formation & geological history
Formed by the accumulation of silica-rich fluids in sedimentary environments or by the replacement of calcium carbonate. Often found as nodules within limestone or chalk.
Uses & applications
Historically used for making stone tools and starting fires (flint). Currently used in road construction, stone jewelry, and lapidary art.
Geological facts
Chert is so hard it will scratch glass. It was one of the first materials used by prehistoric humans to create sharp-edged tools like arrowheads and knives.
Field identification & locations
Identify in the field by its waxy appearance, smooth conchoidal (shell-like) fractures, and its ability to scratch steel. Found globally in sedimentary basins.
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