sedimentary
Chert / Flint
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Brown, tan, gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Brown, tan, gray
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Brown, tan, gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds.
Uses & applications
Historically used for stone tools and weapons (arrowheads); currently used in road construction, as jewelry (jasper varieties), and as a fire-starter (flint).
Geological facts
Flint is a variety of chert that was essential to prehistoric humans for its ability to produce sharp edges. It sparks when struck against steel due to its hardness.
Field identification & locations
Identify by its smooth, waxy surface and characteristic curved (conchoidal) fractures. Found globally, often as nodules in sedimentary basins.
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