sedimentary
Chert (often called Flint)
Chert (Microcrystalline Quartz, SiO2)
Hardness: 7 (Mohs); Color: Tan, brown, gray, or white; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs)
- Color
- Tan, brown, gray, or white
- 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); Color: Tan, brown, gray, or white; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Forms as nodules or layers in limestone or chalk through the accumulation of siliceous remains of organisms (like diatoms or radiolarians) or chemical precipitation from groundwater. It can be found in strata from Precambrian to modern ages.
Uses & applications
Used historically for stone tools (arrowheads, knives) due to its sharp conchoidal fracture. Modernly used as road aggregate, architectural stone, and occasionally for flint-and-steel fire starting.
Geological facts
Chert is so hard it can scratch steel. When struck against steel, it produces sparks, which made it essential for early flintlock firearms and survival kits. This specimen appears to have edges consistent with knapping or natural fracturing.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a knife), waxy appearance, and smooth, curved (conchoidal) breaks. Often found in creek beds or eroding out of limestone cliffs.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary