sedimentary
Chert / Jasper
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Rusty brown to reddish due to iron oxide staining, Luster: Dull to waxy, Crystal Structure: Microcrystalline/Cryptocrystalline, Fracture: Conchoidal (shell-like curves)
- Hardness
- 6
Identified More sedimentary →
Explore Chert / Jasper in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6.5-7 (Mohs scale), Color: Rusty brown to reddish due to iron oxide staining, Luster: Dull to waxy, Crystal Structure: Microcrystalline/Cryptocrystalline, Fracture: Conchoidal (shell-like curves)
Formation & geological history
Formed as a sedimentary rock by the accumulation of silica-rich microfossils (like radiolarians) or through the chemical precipitation of silica in groundwater. This specimen shows significant oxidation (iron staining) from weathering.
Uses & applications
Historically used for stone tools (flint knapping) due to its sharp edges when broken. Modern uses include decorative landscaping, gravel, and occasionally as a lapidary material for polishing.
Geological facts
Chert is so durable that it often survives long after the surrounding rock has weathered away, which is why it is frequently found as rounded river stones or rugged nodules in fields.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its sharp, curved fracture lines. It is found globally in limestone and dolomite formations or as alluvial pebbles in stream beds.
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