sedimentary

Chert (Pebble)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Grayish-tan/brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Grayish-tan/brown
Luster: Waxy to dull

Identified July 14, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Grayish-tan/brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or inorganic precipitation in sedimentary environments. Often found as nodules in limestone or as rounded river/beach pebbles.

Uses & applications

Historically used for stone tools (arrowheads) due to its sharp fracture edges. Today, it is used in construction aggregate, road base, and as decorative river stones.

Geological facts

Chert is extremely durable and chemically stable, which is why it often survives as a pebble long after the surrounding rock has weathered away. Known as 'flint' when found in chalk.

Field identification & locations

Identified by its smoothness, waxy appearance, and ability to scratch glass. Small rounded pebbles like this are ubiquitous in riverbeds, glacial tills, and coastal beaches globally.