sedimentary
Chert (Chert Nodule in Limestone)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Dark brown to black with white/tan matrix, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Identified More sedimentary →
Explore Chert (Chert Nodule in Limestone) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 (Mohs scale), Color: Dark brown to black with white/tan matrix, 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 organic remains (like radiolarians or diatoms) or chemical precipitation within carbonate sedimentary environments. These nodules often displace limestone as they grow.
Uses & applications
Historically used for making stone tools (arrowheads/scrapers) due to its sharp edges; currently used as construction aggregate or as decorative landscape stones.
Geological facts
Chert is so hard it can strike sparks from steel, which led to its extensive use in flintlock firearms. Dark varieties are often specifically referred to as flint.
Field identification & locations
Identify by its waxy luster, extreme hardness (it will scratch glass), and conchoidal (shell-like) fracture pattern. Commonly found embedded in limestone or chalk outcrops.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
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 (primarily SiO2)
sedimentary