sedimentary

Quartz-veined Chert

Silicon dioxide (SiO2)

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

Identified June 25, 2026More sedimentary →

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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.