sedimentary
Chert with Quartz Veining
Microcrystalline silica (SiO2)
Hardness: 7 (Mohs scale), Color: blue-grey base with white crystalline veins, Luster: dull to waxy, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal
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Physical properties
Hardness: 7 (Mohs scale), Color: blue-grey base with white crystalline veins, Luster: dull to waxy, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal
Formation & geological history
Formed from the accumulation of silica-rich organic remains or chemical precipitation in marine environments; subsequently fractured and filled with hydrothermal quartz veins.
Uses & applications
Historically used for making sharp tools and arrowheads; currently used as decorative gravel, in lapidary work, and as a durable construction aggregate.
Geological facts
Chert is so hard it can strike sparks against steel. The white lines across this specimen are quartz veins, which formed when mineral-rich water flowed through cracks in the rock.
Field identification & locations
Look for its extreme hardness (cannot be scratched by a steel knife) and the glass-like conchoidal fracture patterns on broken edges. Common in riverbeds and mountainous terrain.
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