sedimentary
Chert (Flint variety)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, brown, or white; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, brown, 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 on Mohs scale; Color: Gray, tan, brown, or white; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); 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 the chemical replacement of limestone/dolomite by silica-rich groundwater. Often found as nodules or lenses within carbonate rock layers.
Uses & applications
Historically used for stone tools (arrowheads, knives) and strike-a-lights. Modernly used as a decorative stone, road aggregate, and for making high-quality ceramics or as a grinding medium.
Geological facts
Because it fractures conchoidally to produce razor-sharp edges, it was the most important material for early human technology. Flint (a dark variety of chert) was essential for spark-ignition systems in early firearms.
Field identification & locations
Identify in the field by its smooth, waxy surface and its ability to scratch glass. Look for the distinct 'shell-like' curved fracture patterns. It is extremely common in areas with limestone bedrock globally.
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