sedimentary
Chert (Jasper/Agate variety)
Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: tan, white, and brownish, Luster: waxy to vitreous, Crystal Structure: Trigonal (microscopic), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
- Hardness
- 6
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6.5-7 (Mohs scale), Color: tan, white, and brownish, Luster: waxy to vitreous, Crystal Structure: Trigonal (microscopic), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich microfossils or chemical precipitation from silica-rich fluids within sedimentary environments. This specimen shows significant rounding from water erosion (alluvial/beach transport).
Uses & applications
Used historically for stone tools due to its sharp fracture; currently used for landscaping, as semi-precious gemstones when polished, and for geological study.
Geological facts
Chert is so durable that it often survives long after the surrounding rock has weathered away. The brownish patterns in this specimen are likely caused by iron oxide impurities.
Field identification & locations
Identify by its waxy texture, inability to be scratched by a steel knife, and smooth, curved (conchoidal) fracture surfaces. Commonly found in riverbeds and on beaches worldwide.
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