sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: tan, brown, or gray, 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, brown, or gray, Luster: waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Forms through the precipitation of silica from seawater or the accumulation of silica-rich organic remains like sponges and radiolarians. Often found as nodules in limestone or as bedded deposits.
Uses & applications
Historically used for making stone tools (arrowheads). Modern uses include road surfacing materials, decorative landscaping, and as a raw material for silicon production.
Geological facts
Because it breaks with a conchoidal fracture like glass, it produces very sharp edges, which is why it was the primary material for prehistoric weapons and cutting tools.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its waxy luster on fresh broken surfaces. Found globally in sedimentary basins.
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