sedimentary
Chert (Iron-stained)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs, Color: Brown/tan due to iron oxide impurities, Luster: Waxy to dull, Crystal structure: Trigonal (microcrystalline), 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, Color: Brown/tan due to iron oxide impurities, Luster: Waxy to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed by the precipitation of silica from groundwater or the accumulation of silica-rich organic remains in marine environments. This specimen appears weathered and stained by iron oxides over time.
Uses & applications
Historically used for making stone tools (arrowheads). Today used as construction aggregate, road base, and occasionally in lapidary work as tumble-stone.
Geological facts
Chert is so hard it can scratch steel and glass. It was one of the first materials ever traded by early humans because of its predictable fracture and sharp edges.
Field identification & locations
Identify in the field by its waxy luster, extreme hardness, and smooth, curved (conchoidal) breaks. Often found as nodules in limestone or as stream pebbles.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary