sedimentary
Chert (specifically Black Chert or Flint)
Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Dark grey to black; Luster: Dull to waxy; Structure: Cryptocrystalline/Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to waxy
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: Dark grey to black; Luster: Dull to waxy; Structure: Cryptocrystalline/Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by chemical precipitation in marine environments. Often found as nodules or layers within limestone or chalk beds.
Uses & applications
Historically used for stone tools (knapping) and fire-starting. Currently used as a road aggregate, in jewelry (when decorative), and for abrasive purposes.
Geological facts
Chert is so hard it can scratch steel. When struck against steel, it can produce sparks, which made it the primary material for flintlock firearms and ancient survival. It breaks with a conchoidal fracture, creating edges sharper than a surgeon's scalpel.
Field identification & locations
Identify in the field by its smooth, waxy texture and shell-like (conchoidal) curved breaks. It will easily scratch glass. Commonly found in limestone outcrops or as river-worn cobbles.
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