sedimentary

Chert Pebble with Quartz Veins

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 (Mohs scale), Color: Dark grey to charcoal with white veins, Luster: Waxy to vitreous (if wet), Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Hardness: 6

Identified March 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation on the seafloor. The white quartz veins formed later via hydrothermal activity where mineral-rich fluids filled fractures; geological age ranges from Precambrian to Cenozoic.

Uses & applications

Used historically for stone tools due to sharp edges; currently used for decorative landscaping, gravel, and as a material for tumble-polishing for beginning lapidaries.

Geological facts

Dark-colored chert is often called 'Flint.' This specific piece is a river-worn or beach-worn pebble, indicated by its rounded edges. It is a classic example of 'secondary mineral enrichment' where the white veins cross-cut the original rock.

Field identification & locations

Identify in the field by its hardness (it should scratch glass), smooth waxy texture, and the way the white veins cross through the darker matrix. Commonly found in riverbeds, glacial deposits, and coastal beaches globally.

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