sedimentary
Chert (variously known as Flint)
Microcrystalline quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, or brown with a white chalky cortex; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, or brown with a white chalky cortex
- 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, or brown with a white chalky cortex; 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 radiolaria or diatoms) or chemical precipitation in marine environments, often replacing carbonate minerals in limestone.
Uses & applications
Historically used for stone tools and weapons (arrowheads); currently used in road construction, as a filler in cement, and as 'flint' in fire-starting kits.
Geological facts
Chert is so hard it can scratch glass and produces sparks when struck against steel. It was the primary material for the 'Stone Age' technological revolution.
Field identification & locations
Identify by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch steel. Often found as nodules within limestone or chalk beds.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone
Arenite
sedimentary
Sandstone (Quartz-rich)
Arenite (SiO2)
sedimentary