sedimentary

Chert (Beach Pebble)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Greenish-brown with white inclusions; Luster: Waxy to vitreous (especially when wet); Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Greenish-brown with white inclusions
Luster: Waxy to vitreous (especially when wet)

Identified June 24, 2026More sedimentary →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or by chemical precipitation in marine environments. This specimen exhibits water-worn rounding from wave action on a beach or riverbed.

Uses & applications

Primarily used for lapidary work (tumbling and polishing), as gravel in landscaping, and historically for making sharp-edged tools like arrowheads due to its conchoidal fracture.

Geological facts

Chert is one of the most durable sedimentary rocks. When struck against steel, it can produce sparks, leading to its historical use in flintlock firearms and fire-starting.

Field identification & locations

Identified by its extreme hardness (cannot be scratched by a steel knife) and smooth, rounded surface. Commonly found on pebble beaches or in limestone deposits. Look for the waxy texture and shell-like (conchoidal) fracture patterns on any chipped edges.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Chert Breccia

Brecciated Chert (Microcrystalline Silica)

sedimentary

Sandstone

Arenite (primarily SiO2)

sedimentary

Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

sedimentary

Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary

Sandstone

Arenite

sedimentary