sedimentary
Chert (varietal: Flint/Jasper mix)
Hydrous Silica (SiO2)
Hardness: 6.5-7 Mohs; Color: Gray, tan, or brown with possible banding; Luster: Waxy to dull; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
- Hardness
- 6
- Color
- Gray, tan, or brown with possible banding
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Gray, tan, or brown with possible banding; Luster: Waxy to dull; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
Formation & geological history
Formed in marine or freshwater environments by the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from hydrothermal fluids within sedimentary rock layers.
Uses & applications
Historically used for stone tools and weapons (arrowheads); currently used as abrasive media, in construction aggregate, and occasionally as decorative landscaping stone or tumbled pocket stones.
Geological facts
Chert has been used by humans for over 2 million years. When struck against steel or other hard minerals, it can produce sparks, making it essential for early fire-making and flintlock firearms.
Field identification & locations
Identify in the field by its very smooth, glass-like fracture surfaces (conchoidal) and its ability to scratch glass. Found globally in limestone or chalk beds. Collectors look for unique banding or 'nodule' shapes.
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