sedimentary
Chert (specifically Gray/Tan Chert Node)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, brownish-green; Luster: Waxy to dull; Crystal structure: Cryptocrystalline/Trigonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, brownish-green
- 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 on Mohs scale; Color: Gray, tan, brownish-green; Luster: Waxy to dull; Crystal structure: Cryptocrystalline/Trigonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like diatoms or radiolaria) or through chemical precipitation within limestone or chalk beds. This specimen appears water-worn, suggesting it was found in a river or alluvial deposit.
Uses & applications
Historically used for stone tools and arrowheads; currently used as construction aggregate, road base, and as decorative landscape stone. It is also collected as a lapidary material for tumbling.
Geological facts
Chert has been used by humans for millions of years to create sharp-edged tools due to its conchoidal fracture. Some types of chert, like flint, were vital for starting fires in early history.
Field identification & locations
Identify in the field by its smooth, waxy feel, hardness (it will scratch glass), and the way it breaks into curved, shell-like flakes. Found globally in sedimentary basins and riverbeds.
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