sedimentary
Chert (often called Flint)
Microcrystalline to cryptocrystalline quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, gray; Luster: Waxy to dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 6
- Color
- Brown, tan, gray
- 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 Mohs scale; Color: Brown, tan, gray; Luster: Waxy to dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by precipitation from silica-rich groundwater replacing other minerals in limestone or chalk beds.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its conchoidal fracture. Modernly used in construction aggregate and as a spark-generator in flint-and-steel fire starters.
Geological facts
This specimen appears to be a small flake of chert, which was the 'high-tech' material of the Stone Age. It breaks into sharp edges that can be even sharper than a surgical scalpel.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), its waxy feel, and the way it breaks into curved, shell-like shapes (conchoidal fracture). Commonly found in limestone outcrops or as river pebbles.
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