Flint is a hard, tough chemical or biochemical sedimentary rock that breaks with a conchoidal fracture. It is a form of microcrystalline quartz that is typically called “chert” by geologists.

Flint often forms as nodules in sedimentary rocks such as chalk and marine limestones. The nodules can be dispersed randomly throughout the rock unit but are often concentrated in distinct layers. Some rock units form through the accumulation of siliceous skeletal material. These can recrystallize to form a layer of bedded flint.

Flint is highly resistant to weathering and is often found as pebbles or cobbles along streams and beaches. Early people who used flint to make tools often prospected these areas to find nicely shaped pieces of flint for making specific tools.