Everyone knows what a stone
arrowhead looks like; they're so distinctive that they're hard to
miss under most circumstances. But few stone tools are so obvious.
Have you ever been walking through a ploughed field, and found a
broken bit of rock that seemed to have been deliberately shaped?
How about a sharp-edged stone with several flakes gone from one
side, or an unusually smooth fragment of sandstone? If you have,
then you've probably found a prehistoric stone artefact, or at
least a piece of one. Although stone tools may vary in style from
one region to another, they nonetheless conform to a few specific
types all over the world: there are only so many ways you can
grind, break, or otherwise shape stone.
If you're an outdoors person, it's a good idea to be able to recognize stone artefacts, if only so that you can tell your friendly neighbourhood archaeologists where they are. Should you find an artefact, it's best to leave it where it lies, unless it's hopelessly out of context. Physical artefacts are some of the few clues we have about prehistoric cultures, since those cultures left no written records. Because this is the case, you shouldn't disturb any potential archaeological site before it's been properly recorded and tested by professionals. Instead of collecting artefacts from the site, alert the proper authorities -- usually university archaeologists, local archaeological societies, and the Office of the State Archaeologist -- about the location of the site. They may even ask you to fill out a state archaeological site form, which can be an education in its own right.
There are many types of stone artefacts, few of which are as "sexy" as an arrowhead (or "projectile point," to use the scientific term). The shapes, material types, origins, and uses of these artefacts can vary greatly, but they typically fall into three basic types: ground stone, battered stone, and chipped stone.
Ground stone artefacts are those shaped and created by abrasion of the tool stone. The material ground generally consists of a coarse-grained stone, such as sandstone or basalt that is resistant to chipping. Ground stone artefacts can take many forms, including stone axes and adzes, grooved stones used as fishing sinkers or bolas, grinding slabs for processing food, hand tools (often called "manos") used in conjunction with grinding slabs, and ornaments. Because of the nature of many of these tools, it's usually obvious what they were used for. However, if you should find a fragment of a ground stone tool or a grinding slab, its nature may not be so clear; in these cases, look for an exceptionally smooth, possibly shiny surface that seems to have been shaped, either deliberately or incidentally, by human activity. Some such artefacts may have grooves rubbed or scratched into their surfaces. Ground stone tools are occasionally so large as to be non-portable. Battered stone artefacts are exactly what the name implies: tools that bear evidence of having been battered against something else. The most common type of battered stone artefacts are hammer stones, which are hard, rounded stones used for direct fracturing of stone during the creation of chipped stone tools. Battered stone artefacts are usually made of tough stones such as quartzite, basalt, gneiss, limestone and other materials not suitable for chipped stone manufacture.
At many prehistoric sites, the
most common stone tools are made of chipped stone, since chipped
stone tends to be more versatile and holds an edge better than
ground stone. Types of chipped stone you might find include
flakes (as both utilized tools and as chipping waste), unifaces,
and bifaces (including projectile points). The process of
creating chipped stone tools is called "lithic reduction"
or "flint knapping." The first step in lithic reduction
is the procurement of quantities of suitable tool stones. These
most often occur naturally in the form of nodules or cobbles, and
must possess a crypto crystalline, siliceous structure to be
useful; that is, they should be extremely fine-grained and should
display the fracture characteristics of industrial glass. The
best materials, which are often found in streambeds, include
obsidian (a form of natural glass), chert, flint, and chalcedony.
Once the proper material has been selected, a hammer stone is used to direct a sharp blow to the surface of the stone. The energy of this blow propagates through the material in the shape of a cone, causing the rock to fracture in a specified, easily controlled fashion. To visualize this cone of force, think of what happens when a BB hits a plate glass window: a substantial cone-shaped piece of glass flies out of the opposite side of the pane, though the hole on the exterior of the window may be smaller than the BB that created it. This is called conchoidal fracturing. If a flintknapper strikes the tool stone in the proper manner during lithic reduction, the resulting conchoidal fracturing detaches a thin section of material called a flake. In most cases a portion of the cone of force is detached with the resultant flake, leaving a distinctive bulb of applied force on the flake and a corresponding flake scar on the core. In some instances this can be helpful in actually piecing a core back together from its flakes.
So if you find a thin chip of
stone with a slightly thicker bulge on one end, you can be sure
that you've found a flake. Many flakes are blades; a blade is
defined as a specialized flake that is usually at least twice as
long as it is wide. These often served as actual knife blades, as
hide scrapers, or as engraving tools.
The scarred nucleus of tool stone that results from flint knapping is called a core. Cores can come in many different shapes and sizes; a core may manifest as anything from a tiny, exhausted remnant to a chopper-like object with just a few flakes removed from one edge. The goal of lithic reduction can be to manufacture an object or objects from either the removed flakes, the core itself, or both. Cores are, along with flakes, the most obvious evidence of flint knapping. If a variety of tools, but no flakes or cores, is found at a site, then it's safe to assume that no lithic reduction was occurring at the site. Sometimes the types of cores at a site will, along with the waste flakes found, indicate the type of lithic reduction that was occurring there.
Sometimes flakes and core fragments were modified into unifaces. A uniface is a tool that has had flakes systematically removed from one side, producing a sharp edge. Often, the flake scars are tiny, suggesting that they were removed with a very fine point or, occasionally, by the flintknapper's teeth. Sometimes the modification is so minimal that it takes a sharp eye to notice it. Unifaces made from flakes often retain their bulbs of applied force.
Some types of specialized unifaces that may occur include denticulates (saw-bladed unifaces), gouges (used to poke holes in things), and scrapers (used to scrape hides). Scrapers are easily recognizable: they're often made on thick blades with fine flaking on one end, producing a slightly convex, sharp surface. However, scrapers manufactured by the very earliest Native Americans, the Paleo-Indians, are wider than they are long, and very much resemble large human thumbnails. These "thumbnail scrapers" are so unique that they're used as diagnostic markers for Paleo-Indian sites.
Bifaces are tools that display flake scars on both sides. These tools may include choppers, hand-axes, some types of scrapers, and a plethora of other tool types, including projectile points (that is, arrowheads and spear points) and knives. Common types of crude bifaces include blanks, which are large, roughed-out objects that were intended for further reduction at a later time; thinned blanks, which are further along in the reduction process; and preforms, which are unfinished bifaces in an advanced stage of reduction.
Most bifaces are easy to recognize, at least in a general sense. However, it takes a great deal of knowledge and experience to actually identify formalized artefact types. Such identification in extremely important to archaeologists (both avocational and professional) in attempting to identify the culture(s) that left the stone tools behind. The last two centuries of research have resulted in a prehistoric temporal framework for each region of the US, one that is constantly being refined by additional work, and often specific types of stone tools can pinpoint a site's origin in time.
There you have it: the basics to recognizing stone tools. This article merely scratches the surface, to coin a phrase -- lifetimes have been spent on the esoterica of stone tool manufacture -- but it'll give you a rudimentary understanding of the subject. Who knows? Keep your eyes open, and your own recognition of a stone tool may very well contribute to our understanding of the prehistoric timeline for your region.
Honey Flint Arrowhead 5,000BC
This axe head dates from around 3,000 BC
Neolithic Miniature Flint Axe
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