sedimentary
Chert (specifically Flint or Jasper variant)
Microcrystalline quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, and grey; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, and grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, and grey; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed by the precipitation of silica in sedimentary environments, often replacing organic material or filling cavities in limestone. Found in geological formations ranging from Precambrian to recent times.
Uses & applications
Historically used for making stone tools (arrowheads). Currently used in road construction as aggregate, in some ceramics, and as lapidary material for hobbyists.
Geological facts
Chert was one of the most important materials for early humans due to its ability to break into sharp edges like glass. It is so hard that it can scratch steel.
Field identification & locations
Identify by its 'shell-like' conchoidal fracture patterns and the fact it cannot be scratched by a steel knife. Commonly found in riverbeds or limestone outcrops.
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