sedimentary
Chert (specifically Flint or Jasper variant)
Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale). Color: Tan, brown, and grey with possible iron oxide staining. Luster: Waxy to dull. Crystal structure: Cryptocrystalline (microscopic). Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Tan, brown, and grey with possible iron oxide staining
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale). Color: Tan, brown, and grey with possible iron oxide staining. Luster: Waxy to dull. Crystal structure: Cryptocrystalline (microscopic). Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in sedimentary environments. Common in limestone or chalk beds, found in strata ranging from Precambrian to Cenozoic eras.
Uses & applications
Historical use in making stone tools (arrowheads/scrapers) and fire-starting. Modern use in road construction (aggregate), jewelry (when colorful/Jasper), and as a gemstone for tumbling and polishing.
Geological facts
Chert was one of the most vital materials for early humans due to its ability to break with razor-sharp edges. It is extremely chemically stable and resistant to weathering, often found as 'nodules' in softer surrounding rock.
Field identification & locations
Identify by its 'conchoidal' (shell-like) fracture pattern and its ability to scratch glass easily. Look for it in riverbeds, chalk cliffs, or as nodules in limestone. Collectors should look for sharp edges and a waxy surface texture.
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