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In archaeology, a lithic flake is a thin, sharp fragment of stone that results from the process of lithic reduction. Once the proper tool stone has been selected, a fabricator is used to direct a sharp blow to the surface of the stone. The energy of this blow propagates through the material, producing a Hertzian cone of force which causes the rock to fracture in a specified, easily controlled fashion. This action is repeated as the flintknapper detaches the desired number of flakes from the nucleus of source material, which is marked with the negative scars of these flakes. This scarred nucleus is called a core; the surface area of the core which received the blows necessary for detaching the flakes is referred to as the striking platform.
Flakes may be produced by a variety of means. The detachment force may be introduced by percussion (striking the core with a hard object) or by pressure. When a flake is detached from its parent core by either method, a portion of the cone of force caused by the detachment blow is detached with it, leaving a distinctive bulb of applied force on the flake and a corresponding flake scar on the core. The bulbar end is referred to as the proximal end of the flake; the terminal end is referred to as the distal end. The side displaying the bulb of force is called the ventral surface, while the opposite side is the dorsal surface.
On most natural cobbles or nodules of source material, a weathered outer rind called a cortex covers the unweathered inner material. Flakes are often differentiated by the amount of cortex present on their dorsal surfaces, because the amount of cortex indicates what part of the core the flake came from. Primary cortex flakes are those whose dorsal surfaces are entirely covered with cortex; secondary cortex flakes have at least a trace of cortex on the dorsal surface; and tertiary (interior) flakes lack cortex, having derived entirely from the interior of the core. Primary flakes and secondary flakes are usually associated with the initial stages of lithic reduction, while tertiary flakes are more likely to be associated with trimming and bifacial reduction activities.
Prominent bulbs of force generally indicate that a hard hammer percussor (hammerstone) was used to detach the flake; flakes displaying this characteristic are referred to as conchoidal flakes. Hard hammer flakes are indicative of primary reduction strategies (e.g., core reduction, roughing of blanks and preforms, and the like). More moderate and diffuse bulbs indicate the use of a soft hammer fabricator -- such as bone, wood, or antler -- which produces the bending flakes often associated with bifacial thinning and trimming. The relative abundance of each type of flake can indicate what sort of lithic work was going on at a particular spot at a particular point in time.
A blade is a defined as a specialized flake that is usually at least twice as long as it is wide. There are numerous specialized types of blade flakes. Channel flakes are characteristic flakes caused by the fluting of certain Paleo-Indian projectile points; such fluting produced grooves in the projectile points which apparently facilitated hafting. Prismatic blades are long, narrow specialized blades with parallel margins which may be removed from polyhedral blade cores, another common lithic feature of Paleo-Indian lithic culture. Prismatic blades are often triangular in cross section with several facets or flake scars on the dorsal surface.
Other Flake Characteristics
The striking platform is the point on the proximal portion of the flake on which the detachment blow fell; this may be natural or prepared. Termination type is a characteristic indicating the manner in which the distal end of a flake detached from a core. Eraillures, also referred to as "bulbar scars", are tiny flake scars that appear on some bulbs of applied force. The reason they form is not entirely understood. Of those flakes that do exhibit eraillures, very few have more than one.
Many secondary and tertiary flakes display dorsal flake scars, which are simply the markings left behind by flakes detached prior to the detachment of the subject flake.
Blades and flakes can be modified into tools, for example scrapers and burins, which are created by a burin blow on the tip of a blade which produces a chisel-like edge which may have been used for graving and carving wood or bone.
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