sedimentary

Chert (Jasper/Flint Pebble)

Microcrystalline or Cryptocrystalline Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Brown, tan, reddish-brown; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic/none visible); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 7 (Mohs scale)
Color: Brown, tan, reddish-brown
Luster: Waxy to dull

Identified March 22, 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 organic remains (like radiolaria or diatoms) or by the replacement of limestone. Can form in deep marine environments or as nodules in limestone/chalk. Found across all geological ages.

Uses & applications

Historically used for stone tools (knapping) due to its sharp edges. Modernly used in road construction as aggregate, ornamental stones in landscaping, or tumbled for jewelry.

Geological facts

Chert was one of the first materials used by early humans to create survival tools like spearheads and scrapers. Because it breaks into sharp, glass-like shards, it remained essential for thousands of years.

Field identification & locations

Identify by its 'conchoidal fracture' (curved, shell-like breaks) and high hardness (it will scratch glass). This specimen is a stream-worn or weathered pebble found commonly in gravel deposits and river beds throughout the United States and Europe.

Other sedimentary specimens

See all

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