sedimentary
Chert (Flint)
Chert (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, or gray; Luster: Waxy or dull; Crystal Structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, or gray
- Luster
- Waxy or dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, or gray; Luster: Waxy or dull; Crystal Structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed from the accumulation of siliceous remains of marine organisms or through chemical precipitation from silica-rich groundwater within limestone or chalk beds.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) and starting fires; currently used as road aggregate, architectural stone, and sometimes as semi-precious gemstones.
Geological facts
Chert is so hard it can scratch steel. When struck against iron or steel, it produces sparks, which led to its extensive use in flintlock firearms and early fire-making kits.
Field identification & locations
Identify in the field by its smooth, waxy surface and conchoidal (shell-like) fractures with sharp edges. It is commonly found as nodules in limestone or as seafloor deposits.
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