sedimentary
Chert (Grey-Green Flint)
Microcrystalline silicon dioxide (SiO2)
Hardness: 6.5-7 on the Mohs scale. Color: Opaque grey or dull green. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (exhibits conchoidal fracture). Specific gravity: 2.65.
- Hardness
- 6
- Color
- Opaque grey or dull 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: 6.5-7 on the Mohs scale. Color: Opaque grey or dull green. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (exhibits conchoidal fracture). Specific gravity: 2.65.
Formation & geological history
Formed from the chemical precipitation of silica-rich fluids or the accumulation of microscopic skeletal remains of silica-secreting organisms (like diatoms or radiolarians) in marine environments. It is often found as nodules in limestone or chalk beds. Geological age ranges from Precambrian to Cenozoic.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges when fractured. Modern uses include road surfacing, jewelry (when polished), and as a raw material for silicon production.
Geological facts
Chert has a unique property where it produces sparks when struck against steel, which made it essential for early firearms (flintlocks) and fire-starting. It is incredibly durable and chemically stable, often surviving billions of years of weathering.
Field identification & locations
Identify in the field by its characteristic shell-like (conchoidal) fracture pattern and its ability to scratch glass. It often feels smooth or waxy. Common in riverbeds, glacial deposits, and embedded in sedimentary rock layers.
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