sedimentary
Chert (variations include Flint or Jasper)
Aphanitic Silica (SiO2)
Hardness: 7 (Mohs scale), Color: Gray, brown, or tan with waxy luster, Crystal structure: Microcrystalline/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: Gray, brown, or tan with waxy luster, Crystal structure: Microcrystalline/Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation from groundwater within limestone or chalk beds. Commonly found in Paleozoic and Mesozoic strata.
Uses & applications
Historically used for stone tools and starting fires (flint). Currently used in road construction, as an abrasive, and occasionally for lapidary work.
Geological facts
Because it breaks with a conchoidal fracture, it creates edges thinner than a steel scalpel, making it the primary material for prehistoric arrowheads and knives.
Field identification & locations
Identify in the field by its waxy texture, smooth curved (shell-like) fractures, and its ability to scratch glass. Commonly found in riverbeds or eroding out of limestone cliffs.
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
Arenite
sedimentary
Sandstone (Quartz-rich)
Arenite (SiO2)
sedimentary