sedimentary

Chert (Quartz Variety)

Chert (Silicon Dioxide, SiO2)

Hardness: 7 on Mohs scale; Color: Brown, tan, or honey-colored; Luster: Waxy to dull; Crystal structure: Microcrystalline (Cryptocrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 – 2.7.

Hardness: 7 on Mohs scale
Color: Brown, tan, or honey-colored
Luster: Waxy to dull

Identified March 27, 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 by chemical precipitation in marine or groundwater environments. This specimen appears water-worn, suggesting transport in a river or stream bed.

Uses & applications

Historically used for making stone tools (arrowheads/scrapers) due to its sharp edges when broken. Today, it is used as road aggregate, in landscaping, and as a low-cost lapidary material for tumbling.

Geological facts

Chert is so durable that it often survives millions of years of erosion that destroy other rocks. Some chert formations, like the Gunflint Chert, preserve microfossils of the oldest life forms on Earth dating back 2 billion years.

Field identification & locations

Identify in the field by its hardness (it will scratch steel and glass) and its smooth, shell-like (conchoidal) breakage patterns. Often found as nodules within limestone or as river pebbles. Common throughout the American Midwest and globally in sedimentary basins.

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