sedimentary
Chert (Jasper/Flint variety)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Tan, brown, ochre with iron staining; Luster: Waxy to dull (becomes glossy when wet); Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Tan, brown, ochre with iron staining
- Luster
- Waxy to dull (becomes glossy when wet)
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Tan, brown, ochre with iron staining; Luster: Waxy to dull (becomes glossy when wet); Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation from silica-rich fluids in marine or groundwater environments.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to conchoidal fracturing. Modernly used for landscaping, road aggregate, and as a semi-precious gemstone in lapidary work.
Geological facts
Chert is so hard it can scratch glass and steel. It was one of the most important minerals for prehistoric humans due to its ability to hold a sharp edge.
Field identification & locations
Identify in the field by its smooth, waxy texture and sharp, shell-like edges when broken. It is often found as nodules in limestone or as distinct bedded layers.
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