sedimentary
Chert (Flint)
Chert (SiO2)
Hardness: 7 on Mohs scale; Color: typically gray, brown, or tan; Luster: waxy to dull; Crystal structure: cryptocrystalline (microscopic quartz); Cleavage: none, exhibits conchoidal fracture; Specific gravity: approx 2.65.
- Hardness
- 7 on Mohs scale
- Color
- typically gray, brown, or tan
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically gray, brown, or tan; Luster: waxy to dull; Crystal structure: cryptocrystalline (microscopic quartz); Cleavage: none, exhibits conchoidal fracture; Specific gravity: approx 2.65.
Formation & geological history
Formed by the precipitation of silica from water or through the replacement of limestone. It often occurs as nodules or layers within sedimentary rocks like limestone or chalk.
Uses & applications
Historically used for stone tools and starting fires; currently used for road surfacing, as an abrasive, and occasionally in jewelry as cabochons.
Geological facts
Flint was one of the most important resources for prehistoric humans, used to create sharp arrowheads and axe heads. It sparks when struck against steel due to its hardness.
Field identification & locations
Identify in the field by its smooth, waxy feel and the sharp edges produced by conchoidal (shell-like) fracturing. Commonly found in limestone outcrops or as river pebbles.
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