sedimentary
Chert (or Flint)
SiO2 (Microcrystalline Quartz)
Mohs hardness: 7. Color: Tan, beige, and brown. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).
- Hardness
- 7
- Color
- Tan, beige, and brown
- Luster
- Dull to waxy
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Physical properties
Mohs hardness: 7. Color: Tan, beige, and brown. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).
Formation & geological history
Forms as nodules or layers in limestone and chalk. Created through the chemical precipitation of silica-rich fluids or the accumulation of siliceous skeletal remains of marine organisms.
Uses & applications
Historically used for stone tools and fire-starting. Currently used in jewelry (as jasper), rock tumbling, and as road aggregate.
Geological facts
Chert is so hard it can scratch steel and glass. It was one of the first materials utilized by early humans to create spearheads and arrowheads due to its sharp edges when broken.
Field identification & locations
Identified by its extremely smooth, shell-like (conchoidal) fracture and its resistance to scratching. Found globally in sedimentary basins.
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Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
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Clastic Sedimentary Rock Grain (SiO2 dominated)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Sandstone
Arenite (primarily SiO2)
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