sedimentary

Chert / River Pebble

Microcrystalline Silica (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs scale), Color: tan to grayish-brown, Luster: dull to waxy, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.6-2.7

Hardness: 6

Identified March 18, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs scale), Color: tan to grayish-brown, Luster: dull to waxy, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.6-2.7

Formation & geological history

Formed in marine or fluvial environments through the accumulation of silica-rich organic or chemical deposits. This specific specimen has been significantly rounded through mechanical weathering (abrasion) in a high-energy water environment, such as a river or stream bed.

Uses & applications

Primarily used in construction as aggregate for concrete or asphalt. Large quantities are used in landscaping or for decorative garden paths. Historically, chert was used for tool-making (stone points) due to its sharp fracture edges.

Geological facts

Chert pebbles like this are nearly indestructible due to their high silica content. They often survive multiple cycles of erosion, moving from ancient mountain ranges through river systems to modern coastal beaches.

Field identification & locations

Identify in the field by its unusual hardness (it will scratch glass easily) and its smooth, rounded 'water-worn' texture. It is common in riverbeds, glacial tills, and gravel pits worldwide.