sedimentary
Chert (Iron-Stained)
Microcrystalline Silica (SiO2)
Hardness: 7 (Mohs scale), Color: Tan to yellowish-brown due to iron staining, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), 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: Tan to yellowish-brown due to iron staining, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich microfossils or precipitation from hydrothermal fluids within sedimentary rock layers. Its rounded shape suggests it was weathered out from a host rock like limestone and tumbled in a stream or river bed.
Uses & applications
Historically used for stone tools and arrowheads. Currently used as construction aggregate, road base, and occasionally as a tumbling stone for lapidary enthusiasts.
Geological facts
Chert is so hard that it can strike sparks against steel, a property used by ancient people to start fires. Variations including jasper, flint, and agate are all members of the chalcedony/chert family.
Field identification & locations
Identify in the field by its hardness (it can scratch glass), its smooth 'river-rock' texture, and its shell-like (conchoidal) fracture if broken. Commonly found in riverbeds and areas with exposed limestone or chalk.
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