sedimentary

Chert Pebble with Quartz Veining

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 Mohs. Color: dark grey to brownish base with white/translucent veins. Luster: dull to waxy. Structure: cryptocrystalline (microscopic crystals). Fracture: conchoidal (shell-like curves).

Hardness: 6
Color: dark grey to brownish base with white/translucent veins
Luster: dull to waxy

Identified March 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as chemical precipitates in marine environments or through the diagenesis of silica-rich biogenic ooze (diatoms/radiolarians). The white veins occur through later brittle fracturing and secondary mineral infilling by hydrothermal fluids or groundwater.

Uses & applications

Historically used for stone tools (lithics) due to its sharp edges; modern uses include aggregate for road construction and tumbling for decorative garden stones.

Geological facts

Chert is so durable that it often survives as smooth river pebbles long after the surrounding rock has weathered away. The crossing white veins are referred to by collectors as 'crackle' or 'network' patterns.

Field identification & locations

Identify in the field by its hardness (it will scratch glass) and waxy texture. Frequently found in riverbeds, glacial till, and coastal shorelines throughout North America and Europe.

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