sedimentary
Chert (Nodule)
Chert (composition: SiO2)
Hardness: 7 (Mohs), Color: Grey to brownish-grey, Luster: Waxy to dull, Crystal structure: Microcrystalline/Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs), Color: Grey to brownish-grey, Luster: Waxy to dull, Crystal structure: Microcrystalline/Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation within sedimentary rock layers, often limestone. These nodules can be millions of years old, dating from various prehistoric eras.
Uses & applications
Historically used for stone tools (arrowheads). Modern uses include aggregate in road construction and as a gemstone when colorful (Jasper/Agate variations).
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture produces extremely sharp edges, perfect for knives and scrapers.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and waxy, smooth texture with shell-like break patterns. Found globally in limestone beds or as loose gravel in riverbeds.
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