sedimentary
Chert (Jasper/Flint variant)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Brown, tan, and grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Brown, tan, and grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Brown, tan, and grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by chemical precipitation from silica-rich fluids within limestone or chalk beds. Most specimens can range from Precambrian to recent geological ages.
Uses & applications
Historically used for stone tools and starting fires (flint). Currently used in jewelry (as jasper), as a construction aggregate, and as a popular specimen for amateur rock collectors.
Geological facts
Chert is so hard it can scratch steel. Because it breaks with a conchoidal (shell-like) fracture, humans have used it for at least 2 million years to make sharp arrowheads, scrapers, and knife blades.
Field identification & locations
Identify in the field by its extreme hardness, waxy texture, and sharp, curved edges where broken. Commonly found in sedimentary basins, riverbeds, and as nodules within limestone or chalk outcrops.
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