sedimentary
Chert (Flint)
Chert (Microcrystalline Quartz, SiO2)
Hardness: 7 on Mohs scale; Color: typically dark grey, brown, or black with occasional light patches; Luster: waxy to dull; Structure: microcrystalline/cryptocrystalline; Cleavage: none, exhibits conchoidal fracture.
- Hardness
- 7 on Mohs scale
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically dark grey, brown, or black with occasional light patches; Luster: waxy to dull; Structure: microcrystalline/cryptocrystalline; Cleavage: none, exhibits conchoidal fracture.
Formation & geological history
Formed from the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or through the chemical precipitation of silica in groundwater. Often found in nodules within limestone or chalk beds.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) and fire-starting (flint and steel). Modern uses include abrasives and road surfacing.
Geological facts
Flint is a variety of chert that occurs in chalk or marly limestone. Because of its predictable conchoidal fracture, it was one of the most important minerals for early human technological development.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel), waxy texture, and sharp, shell-like (conchoidal) edges when broken. Found globally in sedimentary basins.
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