sedimentary
Chert (Basanite / Flint variation)
Chert (Silicon Dioxide, SiO2)
Hardness: 7 (Mohs scale), Color: Dark grey to black, Luster: Waxy to dull, Crystal structure: Microcrystalline/Cryptocrystalline (Trigonal), Cleavage: None (Conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Dark grey to black, Luster: Waxy to dull, Crystal structure: Microcrystalline/Cryptocrystalline (Trigonal), Cleavage: None (Conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolarians) or chemical precipitation in marine environments. This specimen likely formed during the Paleozoic or Mesozoic eras in deep-sea sediment or within limestone beds.
Uses & applications
Historically used for stone tools and weapons due to sharp edges; currently used as a flux in glass making, road gravel, and by collectors as flint for fire-starting.
Geological facts
Black chert is often called 'basanite' or 'touchstone'; it was historically used by goldsmiths to test the purity of gold by observing the color of the streak left on the stone.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its curved, shell-like 'conchoidal' fracture patterns. Common in limestone regions and as nodules in stream beds.
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