sedimentary
Chert (Jasper/Flint variety)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Dark brown to black with earthy patches; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Dark brown to black with earthy patches
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Dark brown to black with earthy patches; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in marine environments. It often occurs as nodules or layers within limestone or chalk beds.
Uses & applications
Historically used for stone tools and weapons due to its sharp edges when broken. Today, used in construction (road gravel), gemstone tumbling, and as a component in ceramics.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture produces extremely sharp edges, leading to the creation of arrowheads, knives, and scrapers. It is also sparks when struck against steel, leading to the 'flint' name.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture pattern. It often has a waxy feel compared to other sedimentary rocks. Commonly found in riverbeds or coastal erosion areas.
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