sedimentary
Chert (Flint/Chalcedony)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Gray/Bluish-gray with brown inclusions, Luster: Waxy to vitreous, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.65
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 (Mohs scale), Color: Gray/Bluish-gray with brown inclusions, Luster: Waxy to vitreous, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. Common in marine limestone formations where it replaces carbonate minerals over millions of years.
Uses & applications
Historically used for stone tools and fire-starting. Currently used in road construction, as an abrasive, and occasionally in jewelry as tumble-polished stones.
Geological facts
Chert is so hard it can scratch glass and steel. It was the primary material for spearheads and arrowheads for thousands of years due to its shell-like (conchoidal) fracture which creates razor-sharp edges.
Field identification & locations
Identify in the field by its waxy texture, smoothness despite weathering, and razor-sharp edges when broken. Frequently found in riverbeds or eroded limestone outcrops.
More like this
Other sedimentary specimens
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