sedimentary

Chert (specifically a nodule with Chalcendony/Agate banding)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 (Mohs scale), Color: tan, grey, brown, translucent to opaque, Luster: waxy to vitreous, Crystal structure: Trigonal (microcrystalline), Cleavage: none (conchoidal fracture), Specific gravity: 2.6-2.65

Hardness: 6

Identified March 12, 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 through chemical precipitation in carbonate rocks. This specimen likely formed as a nodule within limestone or chalk over millions of years.

Uses & applications

Historically used for making stone tools due to its sharp edges; currently used for lapidary work, landscaping, flint-knapping enthusiasts, and as an industrial abrasive.

Geological facts

Chert and its variety, flint, were among the first materials used by early humans to create fire and weapons. Some cherts contain perfectly preserved micro-fossils of ancient organisms.

Field identification & locations

Identify in the field by its conchoidal (shell-like) fracture patterns and ability to scratch glass. Commonly found in riverbeds, glacial tills, or embedded in limestone cliffs. Collectors look for banding (agate) or translucent 'windows' in the stone.

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