The earliest patterned stone tools found so far come from Hagar, Ethiopia and may be 2.4 million years old. More securely dated stone tools have been found in Omro, Ethiopia, from about 2 million years ago.
These early tools were apparently made by striking a stone with another stone, a technique known as percussion flaking. Both the sharp-edged flakes and the sharp-edged cores (the pieces of stone left after flakes are removed) were used as tools.
If the stone has facets removed from only one side of the cutting edge, we call it a unit-facial tool. If the stone has facets removed from both sides, we call it a bifacial tool.
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1. Flake and Core Tool
When a piece of rock is chipped at convenient corners (flaking) and then used the pieces of stones knocked off are waste flakes and the tool is a core tool. When the reverse is the case, that is, when the piece of stone merely acts as the source of producing flakes and these flakes are further shaped (by retouching) then the shaped pieces are called flake tools while the core is a waste.
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It is obvious that in the case of a core tool the length of sharp border obtained is extremely low in relation to the energy spent on it. Whereas in case of a flake tool the same energy can produce 10 to 20 times more sharp borders. Thus, in terms of efficiency a culture dominated by flake tools can be taken as more advanced than another containing only core tools.
2. Positive Bulb of Percussion
Identification of a flake tool can not be done by mere size as there can be cores smaller than large flakes. Here archaeologists take the use of what is known as the active bulb of percussion. It has been noted that when force enters a stone it imprints an elevated bulb on the inner surface of the flake right under the point where the hammer hits it.
3. Negative Bulb of Percussion
The surface on which the hammer hits a stone is called the striking platform and the point on the point on the platform, where the hammer hits, is called the bulbar scar or flake scar of detachment, the corresponding area on the core is called flake scar. This flake scar on the core maintains a deep point corresponding to the positive bulb and this is called the negative bulb of percussion.
4. Flake and Core Terminology
Since a large flake can always become core in relation to the next flake removed from it, the usage of the terms core and flake becomes relative. Since relative terms are useless in scientific analysis, a flake in archaeology is decided to be any piece of stone which maintains a positive bulb of percussion no matter (a) how small or big it is and also (b) how many flakes may have been removed form this.
5. Original Cortex
The surface of the stone which bears no evidence of human workmanship is called original cortex. Such a surface, in case of a pebble, is much more apparent than on chunks and boulders naturally derived form hills.
6. Retouching
Need to introduce the term retouching in a more specific way. Retouching are medium to small sized chips removed in a contiguous manner along a border. These differ from flaking in only the purpose. While flaking are aimed at removing stone material, that is to thin out or obtain aslope, retouching are aimed at regularizing a border or strengthening it.
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Any uncorked stone flake has razor-sharp borders but these borders are damaged easily. The angle formed by the two faces at a sharp natural border can be as low as 7°-10°. Retouching increases this angle to as much as 20°-30°. The difference of the functional edges in the above two cases is the same as safety razor blade from a sturdy pocket knife.