sedimentary
Chert (Siltstone-Chert mixture)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Dark brown to chocolate; Luster: Dull to waxy; Structure: Cryptocrystalline; Fracture: Conchoidal to sub-conchoidal; Specific Gravity: 2.65
- Hardness
- 6
- Color
- Dark brown to chocolate
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Dark brown to chocolate; Luster: Dull to waxy; Structure: Cryptocrystalline; Fracture: Conchoidal to sub-conchoidal; Specific Gravity: 2.65
Formation & geological history
Formed from the accumulation of siliceous remains of marine organisms or chemical precipitation of silica in deep-sea environments. Often associated with ancient limestone or shale beds.
Uses & applications
Historically used for making stone tools (flintknapping) due to its sharp edges when broken. Currently used as road aggregate, in landscaping, and occasionally as lapidary material.
Geological facts
Chert is so hard it can create sparks when struck against steel. This specific brownish variety is sometimes colloquially called 'jasper' or 'flint' depending on the region.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its smooth, shell-like (conchoidal) fracture pattern. Found globally in sedimentary basins.
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