sedimentary
Chert (Flint Nodule)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs scale; Color: Dark grey, brown, tan; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 Mohs scale
- Color
- Dark grey, brown, tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs scale; Color: Dark grey, brown, tan; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed via the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation in marine or groundwater environments. This specimen shows a weathered outer cortex typical of nodules found in limestone or chalk beds.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges; used as a flint starter for fires; used in some road construction and as decorative garden stones.
Geological facts
Flint is a variety of chert that occurs primarily in chalk and marly limestone. When struck against steel, it produces sparks used to ignite tinder, which was the basis for flintlock firearms.
Field identification & locations
Identified by its extremely smooth, waxy surface on broken faces and its characteristic curved (conchoidal) fracture lines. Commonly found in chalky cliffs, riverbeds, and fields in regions like the UK or various parts of Northern America.
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