sedimentary
Chert (Jasper/Flint variety)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs; Color: Brown, tan, reddish-brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6
- Hardness
- 7 Mohs
- Color
- Brown, tan, reddish-brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs; Color: Brown, tan, reddish-brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6
Formation & geological history
Formed by the precipitation of silica from groundwater or the accumulation of siliceous biological remains (like radiolarians) in sedimentary basins. Often occurs as nodules in limestone or chalk.
Uses & applications
Historically used for stone tools/weapons; currently used in jewelry (as jasper), landscaping, and as a component in construction aggregate.
Geological facts
Chert is so hard it can scratch steel. When struck against steel, it can produce sparks, leading to its historical use as 'flint' in strike-a-light sets and flintlock firearms.
Field identification & locations
Identify in the field by its smooth, shell-like (conchoidal) fracture, waxy texture, and extreme hardness. It won't be scratched by a knife blade. Found in riverbeds and sedimentary outcrops worldwide.
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