sedimentary
Flint
Sedimentary cryptocrystalline quartz (SiO2)
Hardness: 7 on the Mohs scale. Color: Typically dark grey, black, brown, or dark green. Luster: Vitreous to waxy. Crystal structure: Microcrystalline/cryptocrystalline quartz (chalcedony). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.60 to 2.65.
- Hardness
- 7 on the Mohs scale
- Color
- Typically dark grey, black, brown, or dark green
- Luster
- Vitreous to waxy
Identified More sedimentary →
Explore Flint in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 on the Mohs scale. Color: Typically dark grey, black, brown, or dark green. Luster: Vitreous to waxy. Crystal structure: Microcrystalline/cryptocrystalline quartz (chalcedony). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.60 to 2.65.
Formation & geological history
Formed by the chemical replacement of calcium carbonate in limestone or chalk by silica-rich solutions during the diagenesis of sedimentary rock. Can date from millions of years old, commonly associated with Cretaceous chalk deposits.
Uses & applications
Historically used for making stone tools, arrowheads, and firearm ignition mechanisms (flintlocks). Today primarily used for decorative purposes, lapidary work, and sometimes as abrasive grit.
Geological facts
Flint is virtually identical to chert chemically, though 'flint' is traditionally used specifically for the dark varieties found in chalk formations. It produces sparks when struck against steel, which made it crucial for early fire-starting.
Field identification & locations
Can be identified in the field by its conchoidal fracture (smooth, curved breakage patterns), high hardness that scratches glass, and waxy luster. Found worldwide in chalk and limestone strata, frequently in riverbeds or coastal gravels where nodules have weathered out.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Quartz pebble
Silicon dioxide (SiO2)
sedimentary
Fossiliferous Concretion
Septarian Concretion containing Brachiopods/Crinoids
fossil
Generic Pebble / Rock Fragment
Lithic fragment / Weathered rock
sedimentary
Sedimentary Sandstone
Arenite (Sedimentary Rock)
sedimentary
Banded Siltstone / Mudstone Pebble
Siltstone / Argillite
sedimentary