sedimentary
Chert (Jasper/Agate variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Red, tan, and white banding, Luster: Waxy to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture)
- 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: Red, tan, and white banding, Luster: Waxy to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture)
Formation & geological history
Formed through the accumulation of silica-rich microfossils or chemical precipitation from silica-rich fluids in sedimentary basins. This specimen appears to be a weathered fragment of banded chert or jasper common in various geological ages.
Uses & applications
Used historically for stone tools due to its sharp edges; currently used for decorative stone, lapidary work (jewelry), and as a collector's specimen.
Geological facts
Chert is so hard it can strike sparks from steel. Varieties with red coloring from iron oxide are often called Jasper, while translucent banded varieties are called Agate.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in stream beds and coastal gravels.
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