The stone arrowhead represents one of the most enduring and effective examples of early technology, relying entirely on the unique geological properties of select stone materials. The success of this hunting and warfare tool was not about finding the hardest rock, but rather the one that fractured in a predictable and controllable way. This technique, known as lithic technology, allowed early humans to transform raw minerals into precision cutting instruments.
Essential Geological Properties
The primary reason certain stones were chosen for arrowheads is their ability to exhibit a phenomenon called conchoidal fracture. When struck with sufficient force, these materials do not break along natural planes or crystalline boundaries, but instead produce a smooth, curved break resembling the ripple marks of a seashell. This characteristic allowed ancient toolmakers to control the shape and sharpness of the resulting piece with remarkable precision.
The stone needed to be hard, generally rating 6 to 7 on the Mohs hardness scale, to maintain a durable edge. Homogeneity was equally important, meaning the stone lacked internal flaws or coarse grains that could disrupt the fracture pattern. This quality is often found in materials with a microcrystalline or cryptocrystalline structure, where individual quartz crystals are too small to be seen without magnification. These fine-grained materials ensure that the force travels predictably, enabling the controlled removal of flakes to shape the point.
The Primary Lithic Materials
The most common materials used globally were those rich in silica, which readily exhibits conchoidal fracture. Flint and chert are the most widespread examples, both being forms of cryptocrystalline quartz. Flint typically forms in nodules within chalk or limestone deposits and often possesses a glassy luster. Chert is a more general term for this type of rock, sharing the same desirable flaking properties as flint. These materials were valued for their balance of sharpness and durability, making them the standard choice for most stone tools.
Another widely utilized material, particularly in volcanically active regions, is obsidian, which is volcanic glass. Obsidian forms when lava cools so rapidly that mineral crystals do not have time to grow, resulting in an amorphous structure. This glassy composition allows it to fracture into an edge that can be thinner and sharper than modern surgical steel. However, obsidian is more brittle than flint or chert, meaning that while it creates a sharp point, it is more susceptible to breaking upon impact with hard bone.
While flint, chert, and obsidian were preferred, other local materials were often employed when superior stone was unavailable. Jasper, a form of opaque cryptocrystalline quartz, was used across many continents, sometimes requiring heat treatment to improve workability. Locally sourced quartzite, a hard metamorphic rock, and petrified wood (wood replaced by silica) were also used. These materials fractured conchoidally, though they were often less predictable or more difficult to work than high-quality flints and cherts.
Transforming Stone into Tools
The process of turning raw stone into a finished arrowhead is called flintknapping, a technique that exploits the fracture mechanics of the material. This method involves the controlled removal of stone flakes to shape the tool, starting with rough shaping before moving to fine detail. The initial stage uses percussion flaking, where the knapper strikes the stone with a hammerstone or a softer material like an antler billet to remove large flakes. This technique thins the stone and establishes the rough bifacial form of the point.
Once the stone has been thinned to a manageable preform, the knapper switches to pressure flaking for the final, delicate work. This technique involves using a pointed tool, such as antler tine or bone, to apply precise, static pressure to the edge of the stone. Instead of striking, the knapper presses inward and downward to detach small, thin flakes. This process creates the final sharp edges, serrations, and notches for hafting onto the arrow shaft.