sedimentary
Chert with Quartz Veining
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: Dark grey to black matrix with white veins, Luster: Waxy to dull matrix/vitreous veins, Crystal structure: Microcrystalline (Cryptocrystalline), Cleavage: None (Conchoidal fracture)
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Physical properties
Hardness: 7 (Mohs scale), Color: Dark grey to black matrix with white veins, Luster: Waxy to dull matrix/vitreous veins, Crystal structure: Microcrystalline (Cryptocrystalline), Cleavage: None (Conchoidal fracture)
Formation & geological history
Formed from the accumulation of silica-rich organic remains (radiolarians or diatoms) or chemical precipitation in marine environments. The white veins are quartz that filled cracks during secondary hydrothermal activity.
Uses & applications
Historically used for stone tools and strike-a-lights. Currently used as decorative landscaping stone, in construction aggregate, or as a lapidary material for polishing.
Geological facts
Dark, fine-grained chert is often referred to as 'Flint.' The white veins seen here indicate the rock underwent tectonic stress, creating fractures that were later sealed by mineral-rich fluids.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel nail) and the way it breaks with smooth, curved surfaces. Common in riverbeds, glacial tills, and marine sedimentary outcrops.
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