Raw materials:
Lithic, or chipped stone, tools can be made only from a few specific types of rock, all of which are composed largely of silica (SiO2). These rocks are either amorphous, meaning that the minerals that compose the rocks have not formed crystals, or cryptocrystalline, meaning that the minerals have formed patterns of microscopic crystals. Flint and chert are cryptocrystalline, composed of tiny needlelike quartz crystals; rhyolite and basalt can also be cryptocrystalline, composed of larger quartz crystals combined with other nonsilica mineral crystals; and obsidian, or volcanic glass, is composed of a combination of amorphous silica and nonsilica minerals. Because these rocks are not composed of large crystalline minerals, they break much like common glass, yielding conchoidal fractures.

A conchoidal fracture is one in which the fracture surfaces are curved. When the rock is struck the energy of the blow is distributed evenly, in a radial fashion, away from the point of contact. This property of fracturing conchoidally is what makes the production of lithic tools possible.

Definitions:
The practice of producing lithic tools is generally termed flintknapping. Initially, a stone, the core, is struck, to break off smaller pieces, flakes. Depending on the technology of the flintknapper, either the core or a flake may then be worked into a finished tool. The flat surface at the top of the flake where it was struck is called the platform. The platform end is the proximal end of the flake; the end where the flake terminates is the distal end. The interior surface of a flake, i.e. the surface that was next to the core, may be called the ventral surface; the exterior surface may be called the dorsal surface. Concave surfaces on any stone where flakes have been removed are called flake scars. Any of the original weathered surface of the stone remaining on the flakes or core is called cortex. The waste products of flintknapping, including unwanted flakes, are called debitage.

Techniques:
Due to conchoidal fracture properties, flakes and cores tend to have distinctive characteristics that vary with the flintknapping techniques used to produce them. The three most common techniques are (1) hard hammer percussion, (2) soft hammer percussion, and (3) pressure flaking. Note that with any technique, because the interior surface of the flake and the corresponding surface of the core or unfinished tool were created by a single fracture, all of the characteristics of flakes also appear in an exact negative impression on the core or unfinished tool.

Hard hammer percussion is the earliest and most basic flintknapping technique, producing flakes by striking another stone, the hammerstone, against a core. It can be used to produce finished, but simple, lithic tools from cores, such as the early handaxes used by Homo erectus, or as a starting point for more elaborate tools formed either from cores or flakes. A flake struck using hard hammer percussion frequently has a crushed area on the platform called a point of percussion. Beneath this on the interior surface of the flake, there will be a swelling, called the bulb of percussion, caused by the force of the striking blow. Sometimes a chip, called an erailleur scar, is knocked off of the bulb of percussion by the blow. Beneath the bulb of percussion, the force of the blow may have created ripples in the fracture which center around the bulb of percussion.

Soft hammer percussion produces flakes by striking the unfinished tool with a soft hammer, usually a piece of antler, bone, or wood. A soft hammer flake differs from a hard hammer flake in that it tends to be thin and flat with a small platform, a lip on the interior of the platform, and a low diffuse bulb of percussion. Because soft hammer percussion is the easiest way to remove large, thin flakes, is particularly useful in producing thin bifaces, or lithic tools that have been worked on both sides.

Pressure flaking produces flakes by using a flaker made of a soft material, such as antler, bone, wood, or copper to apply force by pressing rather than striking. Pressure flakes are small and fragile, and are used to thin and shape lithic tools. Many lithic tools are produced by a combination of all three techniques, with hard hammer percussion followed by soft hammer percussion and then finished by pressure flaking.

Illustrating Stone Tools:
Aside from actually flintknapping,one of the best ways to understand the structure of a stone tool is to illustrate it. Not only will this increase your understanding of stone tools, it is also an extremely useful skill for an archaeologist. Because visual representations of stone tools are highly representational, even someone with limited artistic ability should be able to draw a decent illustration that accurately portrays the structure of the tool.

Lithic illustrations follow a set of conventions that enables the viewer to see the structure of the tool. An accurate outline of the tool is drawn first, using calipers or another measuring device and frequently aided by a scanned image of the tool. Next, the outlines of the flake scars are drawn in, attention being paid to the shape of the scar and its boundaries. There may be much variation in the size and shape of the flake scars, ranging from hard and soft hammer scars that can reach across an entire surface to tiny pressure flaked edge scars. Note that flake scars almost invariably begin at the edge of the tool, but, as earlier scars are overlain and covered by later scars, the earlier scars may appear to originate somewhere in the center. Both the outline of the tool and the outline of the flake scars are drawn with a heavy line. Once the outlines of the flake scars are drawn in, ripples from the force of the blow are added in lighter lines. These enable the viewer to determine how the flake fracture progressed through the tool. Any cortex that is present will also be drawn in as a region shaded by stippling, or dotting.

Exercise: