sedimentary

Chert (Beach Pebble)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: White, cream, and tan with iron-oxide staining; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture).

Hardness: 7 (Mohs scale)
Color: White, cream, and tan with iron-oxide staining
Luster: Dull to waxy

Identified July 4, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: White, cream, and tan with iron-oxide staining; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture).

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments; this specimen has been water-worn into a smooth cobble.

Uses & applications

Used historically for stone tools due to its sharp fracture; currently used for landscaping, aggregate, and as a decorative beach pebble.

Geological facts

Chert is extremely durable and chemically stable, which is why it often survives as rounded pebbles on beaches long after softer surrounding rocks have eroded away. The tan 'swirls' are likely due to rhythmic precipitation of iron oxides, similar to the process that forms Liesegang rings.

Field identification & locations

Identify in the field by its hardness (it will scratch glass and steel) and its smooth, waxy texture. Highly common in coastal areas and riverbeds globally.