sedimentary

Chert (specifically var. Flint or Jasper-rich Breccia)

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale); Color: Gray, tan, and reddish-pink patches in this specimen; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Gray, tan, and reddish-pink patches in this specimen
Luster: Waxy to dull

Identified March 26, 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 precipitation of silica from groundwater or as a biochemical sediment on the ocean floor, filling voids in limestone or replacing carbonates. This specific specimen appears brecciated, likely formed in a high-pressure fault zone or collapse structure.

Uses & applications

Historically used for stone tools and weapons due to sharp edges; currently used for road surfacing, grinding media in industry, and occasionally as semi-precious gemstones (jasper).

Geological facts

Chert is so hard it can strike sparks from steel, a property that led to its use in flintlock firearms. It is incredibly durable and can survive millions of years of erosion.

Field identification & locations

Identify in the field by its hardness (cannot be scratched by a steel knife) and its curved, glass-like 'conchoidal' fracture patterns. Common in limestone regions and creek beds.

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