sedimentary
Chert (Jasper variety)
Silicon Dioxide (SiO2)
Hardness: 6.5–7 on Mohs scale; Color: Dull purple-grey to brown; Luster: Waxy to dull; Crystal structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 6
- Color
- Dull purple-grey to brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Dull purple-grey to brown; Luster: Waxy to dull; Crystal structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) on the seafloor or via chemical precipitation from silica-rich fluids in limestone/dolomite cavities. It can range from Precambrian to recent ages.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges. Modern uses include landscaping, construction aggregate, and as a semi-precious gemstone when polished (Jasper).
Geological facts
Chert was one of the most important materials for early humans to create arrowheads and scrapers. Because of its hardness, it can create sparks when struck against steel, similar to flint.
Field identification & locations
Identify by its waxy texture and its tendency to break with smooth, curved surfaces (conchoidal fracture). It will not be scratched by a steel knife. Commonly found in riverbeds or within limestone outcrops.
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