sedimentary
Chert (Jasper/Flint variety)
Microcrystalline silicon dioxide (SiO2)
Hardness: 7 Mohs scale; Color: Tan, brown, and grey mottled; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 Mohs scale
- Color
- Tan, brown, and grey mottled
- Luster
- Waxy to dull
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 Mohs scale; Color: Tan, brown, and grey mottled; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. This specific specimen appears to be a water-worn river cobble.
Uses & applications
Historically used for stone tools and weapons due to its sharp edges when broken. Currently used for landscaping, road aggregate, and as a lapidary material for polishing and jewelry.
Geological facts
Chert is so durable that it often survives long-distance transport in rivers and glacial deposits, which is why it is frequently found as rounded cobbles far from its original bedrock source.
Field identification & locations
Identify in the field by its hardness (it should scratch glass), waxy luster when wet, and distinctive conchoidal (shell-like) fracture patterns. Frequently found in riverbeds and gravel pits.
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