Flint is composed of tiny crystals of a very hard mineral called silica. The shape of the crystals means that flint can be split, leaving razor-sharp edges. Humans have taken advantage of this to make tools since our earliest history, around four million years ago. The first people to settle in Britain, some 700,000 years ago, brought with them the knowledge of how to make flint tools.

Creating tools

Making a flint tool is a sophisticated process, requiring skill and judgment. The toolmaker, called a "knapper", must select a piece of flint which will not shatter when it is struck. This is done by carefully inspecting the flint for flaws. He must then know exactly where to strike it, and with how much force. The first blow, made with a hard "hammer stone", is the trickiest, for its angle must be correct to make a flake break off. Once this has been achieved, the work gets easier, for there are now ridges on the flint to aim at. In the later stages, softer hammers are used, made of wood or antler, which allow for greater precision. For the final shaping of the tool, the knapper uses pressure-flaking, in which a piece of antler is placed against the edge of the flint, and inward pressure is applied to make small, thin flakes split away.

The most important flint tool was the large, leaf-shaped "hand axe", invented in Africa around 1.6 million years ago. Despite its name, this was an all-purpose tool, used for butchering meat as well as tree felling. Early people also made flat scrapers for removing flesh from hide. Around 40,000 BC, someone discovered that the waste flakes made in knapping could themselves be used as blades, such as arrow heads, or mounted in wooden and bone handles to make a variety of specialised tools.

Flint miners

The earliest tools were made from flints found on the surface. The problem with surface flints is that they have been rolled by rivers and glaciers, and repeatedly frozen in ice ages, making them weak and liable to break. By around 4,500 BC, people learned that better quality flint lay in seams beneath the chalk, and they began to mine for it. Using shovels made from the shoulder blades of deer, and picks made from antlers, they dug deep shafts until they reached the seams of black flint. The miners then tunnelled out side galleries, leaving columns of chalk to support the gallery ceilings. They worked by the light of oil lamps - lumps of chalk hollowed out to hold animal fat or oil. The ceilings of ancient flint mines are often stained black with soot from such lamps.

Polished flint

Some time around 4,000 BC, people began to grind and polish their flint axes to give them smooth surfaces. They used finely grained polishing stones, or pastes made from sand and water. It takes a very long time to polish a hand axe, and the aim was to make a beautiful object rather than an efficient tool. Many polished axes were made from veined flint, which is as beautiful as marble, but would have shattered if anyone tried to use it as a tool. Such axes were the status symbols of the Neolithic ("New Stone") Age, and they were widely traded across northern Europe.

See polished flint axe heads here

New uses for flint

Flint tool-making came to an end in Britain between 1200 and 500 BC, as a result of the widespread adoption of iron. From Roman times, flint was used as a building stone, bonded by lime mortar made by burning chalk and mixing it with sand and water. The lower walls of many Roman buildings are made of flint, whose source was nodules collected from fields after ploughing.

Yet another use of flint was to make fire, by striking it against other materials to produce sparks. In the Stone Age, the material used were a rock called pyrite, later replaced by iron and steel "strike-a-lights". The same fire-making property of flint was used to make the flintlock pistols and muskets of the 17th century.

Flint continued to be used as a building material throughout the Middle Ages, at first for castles, churches and large barns, and later for houses. From the 14th century, stonemasons learnt to knap flint to make square blocks, which could be combined with other types of stone to make decorative patterns. Look out for flint buildings across the chalk counties of Norfolk, Suffolk, Dorset, Sussex and Kent.