sedimentary
Chert (Common Variety)
Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Cream, tan, and beige; Luster: Waxy to dull; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Cream, tan, and beige
- 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: Cream, tan, and beige; Luster: Waxy to dull; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed primarily through the chemical precipitation of silica-rich fluids or the accumulation of siliceous skeletal remains (like diatoms or radiolarians) within deeper marine sedimentary layers. This specimen likely dates from the Paleozoic or Mesozoic eras.
Uses & applications
Historically used for stone tools and arrowheads; currently used in construction aggregate, road surfacing, and as a semi-precious stone for lapidary tumbling.
Geological facts
Because it fractures with sharp edges, chert was one of the most vital materials for early humans to create survival tools. It is also known as flint when found in chalk or marly limestone deposits.
Field identification & locations
Identified in the field by its extreme hardness (cannot be scratched by a steel blade) and its smooth, shell-like fracture surfaces. Frequently found in limestone stream beds or as nodules in rocky outcrops.
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