sedimentary
Chert (Flint)
Microcrystalline or cryptocrystalline quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, brown, black, or tan; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, brown, black, or tan
- 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, brown, black, or tan; 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 chemical precipitation from silica-rich fluids in limestone or chalk beds. It can date from the Precambrian to Holocene.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp conchoidal fracture. Modern uses include road surfacing, high-quality gemstones (when colorful), and fire-starting strikers.
Geological facts
Flint is a variety of chert that occurs in chalk or marly limestone. Because it produces sparks when struck against steel, it was the primary mechanism for ignition in flintlock firearms.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its characteristic shell-like (conchoidal) fracture pattern. Commonly found in riverbeds or as nodules within limestone outcrops.
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