sedimentary
Chert / River Pebble
Microcrystalline Silica (SiO2)
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 More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
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.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone (Quartz-rich)
Arenite (SiO2)
sedimentary
Sandstone (with man-made markings)
Arenite (composed primarily of Quartz, SiO2)
sedimentary