sedimentary

Chert (Flint Nodular)

Chert (Silicon dioxide, SiO2)

Hardness: 7 (Mohs scale); Color: Tan, brown, gray, and cream with a waxy/dull luster; Crystal structure: Microcrystalline/cryptocrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Tan, brown, gray, and cream with a waxy/dull luster

Identified March 31, 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 diatoms or radiolaria) or chemical precipitation within limestone or chalk beds. Often found as nodules within marine sedimentary layers ranging from the Precambrian to recent eras.

Uses & applications

Historically used for stone tools (knapping) and fire-starting (flint). Currently used as a gemstone (Jasper/agate variety), in construction aggregate, and by mineral collectors.

Geological facts

Chert is so hard it can scratch glass and steel. It was one of the most vital resources for early humans to create sharp-edged tools like arrowheads and scrapers due to its predictable conchoidal fracture.

Field identification & locations

Identify by its 'waxy' or 'greasy' feel on smooth surfaces, high hardness, and curved (shell-like) fracture patterns. Frequently found in riverbeds, glacial Till, or eroding out of limestone cliffs.

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