sedimentary
Chert / Flint
Silicon dioxide (SiO2)
Hardness: 7 on the Mohs scale. Color: White, grey, light tan, or brown. Luster: Waxy to vitreous. Crystal structure: Microcrystalline quartz (chalcedony). Cleavage: Conchoidal fracture with no true cleavage. Specific gravity: 2.60 to 2.65.
- Hardness
- 7 on the Mohs scale
- Color
- White, grey, light tan, or brown
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on the Mohs scale. Color: White, grey, light tan, or brown. Luster: Waxy to vitreous. Crystal structure: Microcrystalline quartz (chalcedony). Cleavage: Conchoidal fracture with no true cleavage. Specific gravity: 2.60 to 2.65.
Formation & geological history
Forms in marine environments by the replacement of calcium carbonate in limestone or chalk by silica from sponge spicules or radiolaria, or through direct chemical precipitation of silica gels on the sea floor.
Uses & applications
Historically used for making stone tools, arrowheads, and fire-starting (flint and steel). Today used as aggregate in construction, road metal, and abrasives.
Geological facts
Chert and flint are chemically identical; the term 'flint' is often used specifically for darker varieties found in chalk formations.
Field identification & locations
Easily identified by its distinctive conchoidal fracture (curved, shell-like breaking pattern), waxy luster, and high hardness that can easily scratch glass.
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