sedimentary
Chert (Jasper/Black Chert)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: Dark grey to black with brown weathering rind, Luster: Waxy to dull, Crystal structure: Microcrystalline/Cryptocrystalline (trigonal), 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: Dark grey to black with brown weathering rind, Luster: Waxy to dull, Crystal structure: Microcrystalline/Cryptocrystalline (trigonal), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from hydrothermal fluids in deep-sea or sedimentary environments. Most specimens range from Precambrian to Cenozoic eras.
Uses & applications
Historically used for stone tools/weapons (arrowheads); currently used in construction aggregate, landscaping, lapidary arts (tumbled stones), and as a silica source in glassmaking.
Geological facts
Chert is a variety of quartz that was the 'high-tech' material of the Stone Age because it fractures consistently into sharp edges. Black chert is often called 'flint' if it occurs in chalk or limestone beds.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture pattern. Commonly found in riverbeds, glacial deposits, and as nodules within limestone or dolomite cliffs.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary