sedimentary
Flint (within Limestone matrix)
Silicon dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Black to dark grey interior with a tan/white chalky exterior; Luster: Vitreous to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Black to dark grey interior with a tan/white chalky exterior
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Black to dark grey interior with a tan/white chalky exterior; Luster: Vitreous to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed as nodules or masses in sedimentary rocks like chalk and limestone through the replacement of calcium carbonate by silica-rich fluids. Often dated to the Cretaceous period.
Uses & applications
Historically used for stone tools and weapons (arrowheads/knives); used today as an abrasive, in road construction, and for manufacturing glass and ceramics. Also used as a fire starter.
Geological facts
Flint was the primary material for the Stone Age tool industry. The sharp edges created by its conchoidal fracture can be thinner and sharper than a surgical steel scalpel.
Field identification & locations
Identify in the field by its smooth, glass-like interior revealed by cracks, and its distinctive curved (conchoidal) fracture pattern. It often produces sparks when struck against steel. Commonly found in chalk or limestone deposits.
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