sedimentary
Chert (or Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 on the Mohs scale. Color: Varies from white, grey, brown to yellowish-tan (often called chert when lighter/earthy and flint when dark). Luster: Waxy to dull. Crystal structure: Microcrystalline or cryptocrystalline quartz (chalcedony). Cleavage: None, fractures conchoidally.
- Hardness
- 7 on the Mohs scale
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on the Mohs scale. Color: Varies from white, grey, brown to yellowish-tan (often called chert when lighter/earthy and flint when dark). Luster: Waxy to dull. Crystal structure: Microcrystalline or cryptocrystalline quartz (chalcedony). Cleavage: None, fractures conchoidally.
Formation & geological history
Forms in marine environments through the replacement of calcium carbonate in limestone or chalk by silica-rich solutions, or through the accumulation of siliceous skeletal remains of microscopic organisms like radiolarians and diatoms. Geological age ranges from Precambrian to recent.
Uses & applications
Historically used for making stone tools, arrowheads, and fire-starting (striking against steel). Modern uses include abrasives, road aggregates, and decorative landscaping.
Geological facts
Chert and flint are chemically identical, differing mainly in color and where they are found. Flint traditionally refers to nodules found in chalk formations, while chert refers to deposits in limestone.
Field identification & locations
Easily identified by its conchoidal fracture (smooth, curved breakage patterns similar to broken glass) and extreme hardness that can easily scratch glass. Found worldwide in sedimentary rock formations.
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