sedimentary
Flint
Sedimentary cryptocrystalline quartz (SiO2)
Hardness: 7 on the Mohs scale. Color: Dark brown, grey, or black with a waxy to vitreous luster. Structure: Cryptocrystalline, breaking with a distinct conchoidal fracture. Specific gravity: 2.60 to 2.65.
- Hardness
- 7 on the Mohs scale
- Color
- Dark brown, grey, or black with a waxy to vitreous luster
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Physical properties
Hardness: 7 on the Mohs scale. Color: Dark brown, grey, or black with a waxy to vitreous luster. Structure: Cryptocrystalline, breaking with a distinct conchoidal fracture. Specific gravity: 2.60 to 2.65.
Formation & geological history
Formed through the chemical replacement of calcium carbonate in limestone or chalk by silica-rich solutions during deep burial and diagenesis, typically occurring over millions of years.
Uses & applications
Historically used for prehistoric stone tools, weapons, and fire-starting (strike-a-light). Currently used in decorative landscaping, abrasive grits, and ball mills.
Geological facts
Flint and chert are essentially the same mineral, but 'flint' traditionally refers specifically to the dark nodules found embedded in chalk formations.
Field identification & locations
Easily identified by its dark, smooth, weathered exterior, conchoidal fracture revealing a waxy interior, and high hardness capable of scratching glass. Commonly found along chalk cliffs and beaches.
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