Flint is a sedimentary rock, specifically a hard, fine-grained variety of chert made of microcrystalline quartz (silica).

Rock type in a nutshell

  • Flint is a sedimentary rock.
  • More precisely, it is a cryptocrystalline (very fine‑grained) form of quartz.
  • Geologists usually classify it as a variety of chert that forms in chalk or limestone.

How geologists describe it

  • Composition: mostly silicon dioxide (SiO₂), the same mineral as quartz.
  • Texture: extremely fine-grained, smooth, and homogeneous, often called cryptocrystalline or microcrystalline.
  • Typical host rocks: occurs as nodules or layers in chalks and limestones.

Why people sometimes get confused

  • Some people call any similar silica rock “flint,” but the stricter term is “chert” for the broader group and “flint” for the type found in chalk or marl.
  • In everyday language, both words are often used interchangeably, which is why you may see both “flint” and “chert” in forum discussions and guides.

TL;DR: Flint is a hard, fine‑grained sedimentary rock made of microcrystalline quartz, considered a specific variety of chert that forms in chalky limestones.

Information gathered from public forums or data available on the internet and portrayed here.