sedimentary
Quartz-veined Chert
Silicon dioxide (SiO2)
AI-generated identification · may be incorrectHardness: 7 (Mohs scale), Color: Dark grey/black with white veins, Luster: Waxy to vitreous, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Dark grey/black with white veins, Luster: Waxy to vitreous, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed from silica-rich precipitates in deep-sea environments. The white veins are later secondary quartz fill in rock fractures. These rocks can range from Precambrian to Cenozoic in age.
Uses & applications
Used historically for stone tools due to sharp edges; currently used as aquarium decor, construction aggregate, and by hobbyist lapidaries for tumbling.
Geological facts
Chert is so hard it can strike sparks from steel. Veined varieties like this are often smoothed by river or beach action into 'wishing stones' or 'lucky pebbles.'
Field identification & locations
Identify by its waxy texture and inability to be scratched by a steel knife. Frequently found in riverbeds and coastal beaches in tectonic regions around the world.
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