sedimentary
Chert (Jasper/Flint variety)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs); Color: Tan, brown, and grey mottled; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Tan, brown, and grey mottled
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Tan, brown, and grey mottled; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in sedimentary environments. Can be Paleozoic to Cenozoic in age.
Uses & applications
Historically used for making stone tools (arrowheads/scrapers) due to its sharp edges; used today as a decorative stone, in construction aggregate, or for lapidary work.
Geological facts
Because chert breaks with a conchoidal fracture like glass, it creates edges that are sharper than a surgeon's steel scalpel. It is one of the most common materials used for prehistoric artifacts.
Field identification & locations
Identify by its extreme hardness (will scratch glass), waxy feel, and smooth curved surfaces where it has chipped. Common in limestone or chalk deposits globally.
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