sedimentary
Chert (Jasper variety)
Silicon Dioxide (SiO2) with iron oxide impurities
Hardness: 6.5-7 (Mohs scale); Color: Brown, red, greyish-tan; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5–2.8
- Hardness
- 6
- Color
- Brown, red, greyish-tan
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Brown, red, greyish-tan; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5–2.8
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria) or chemical precipitation from hydrothermal fluids in marine environments. Often found in Precambrian to Cenozoic strata.
Uses & applications
Used historically for stone tools, currently used in landscaping, road aggregate, and as a semi-precious gemstone for jewelry when highly patterned or colored.
Geological facts
Chert was one of the first materials utilized by early humans for tool-making because it breaks into sharp, glass-like edges. The reddish-brown color in this specimen is typically caused by the presence of hematite (iron oxide).
Field identification & locations
Identify in the field by its hardness (it will scratch glass and steel) and its characteristic conchoidal (shell-like) fracture patterns. Frequently found in limestone nodules or as bedded deposits.
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