Lithic material can altered by natural processes so that they sometimes resemble tools. Such lithics are known as eoliths. Also some lithic material can appear to be polished by agencies such as wind and sand, often referred to as desert polish. Also debitage can be altered by natural processes such as heat, frost and patination.
Lithic material can altered by natural processes so that they sometimes resemble tools. Such lithics are known as eoliths. Also some lithic material can appear to be polished by agencies such as wind and sand, often referred to as desert polish. Also debitage can be altered by natural processes such as heat, frost
Water can affect the quality of the rock and water rolling might wear down human traces of use.
Rocks exposed to sun over a long period of time can loose much of its humidity. This process can make them brittle and porous and more difficult to control during production.
Due to heating of the water inside rocks they can crack. Another alteration caused by heat/fire is a change of color. Flint, for example, can become white. A typical heat-fracture is called potlid.
Potlids are small, rounded splinters which pop off the surface of a rock and leaves a concave, irregular scar. Potlids indicate that a raw material is damaged. Potlids can look like a common flake, but a closer look will show that they do not have a platform (Whittaker 1994:73)
"Pot lids are plano-convex flakes that leave a concave scar. These are the result of differential expansion and contraction of isotropic material but are minus the compression rings of force lines usually associated with these conditions. Generally they are a natural occurrence rather than intentional results of man-made flakes" (Crabtree 1982:49).
Fire-cracked rocks are produced by the heating of water in the flint which then forces off pieces. The same process as Heat fracture often resulting in pot lid fractures. The same process as Heat fracture often resulting in pot lid fractures. Futher heating will cause severe cracking of the flint surface and changes in colour first blue, and then as the temperature increses, white.
Fracture caused by frost is due to water that expands inside the rock or as cracks on the surface of it. When the water melts the rock cracks. This freezing-melting process can go one for a long period of time and deteriorate the quality of the rock until it cracks into irregular fragments. A raw material with frost-damage is difficult to control during production of tools.
Frost fracture is caused by water within the flint (or in cracks in the flint surface) freezing and so expanding. When the water melts pieces of flint break off the nodule. This freeze-thaw action can continue through the depositional history of artifacts. Also natural nodules of flint may be 'flaked' by frost action to give the appearance of being deliberately knapped, e.g.starch fractures
Starch fractures occur from freeze- thaw action along planes in the flint sometimes appearing as if blades have been deliberately removed and sometimes leading to such natural objects being classified as blade cores.
A combination of sand and wind can polish a rock surface which gives it a lustre surface which can be seen with the naked eye. The combination of sand and wind can further wear down an artefact to the extent that traces from prior work from human hand is lost.
Desert polish is created by a combination of wind and sand. The movement of sand across exposed flint surfaces polishes the surface to a high gloss that can be seen by the naked eye. It can have the appearance of sickle gloss except that the polish is all over the surface.
Sickle gloss is a use wear polish created by using tools for cutting cereals and therefore is a use-wear polish. It is visible to the naked eye, but only occurs on the used edge, not all over like desert varnish.
Many rocks, especially flint, will due to physical (water) and other chemical influences develop a thin patina on the surface. This patina often causes a change in color and not necessarily a change in the morphology of the rock itself.
"Many cherts and flints will patinate, developing a weathered surface as water and sometimes chemical stains work their way into the flint and as silica and other materials are leached out, producing a thin patina or rind of a different color" Whittaker 1994. , 70
Flint which looks humanly struck can turn out to be ballast. That is flint used as dead freight on ships and dumped at a later stage.
Flint that may appear to be humanly struck can sometimes be ballast, that is flint that was used as ballast on ships which has subsequently been discarded.
Edges of tools can be damaged by natural disturbance after the site has been left. This can be animal activity; animals that dig in the earth or animals that passes through the site and trample on the artefacts, frost in the ground can make the artefacts move, and so do roots etc. Postdepositional disturbance should be accounted for in the interpretation of an artefact.
When flakes have been removed from the edge of a blank by natural processes this can (and often is) confused with retouch. There are various sources of edge damage:
Trampling during occupation of the site;
Post depositional movement in the sediment;
Rough handling during excavation, e.g.. trowel damage;
Storage conditions, e.g.. 'box damage' (if flints are kept loose in a box they can rub together often causing fractures along the edges.
"Edge damage: The removal of material from edges by natural processes, spontaneous retouch, soil movement, trampling etc." as opposed to, "Edge wear: The removal of material from edges by flaking and/or rounding by use." (Grace 1989,, 114) It is impossible to reliably tell the difference between edge damage and edge wear without using special techniques such as use-wear analysis.(see Grace 1989, Grace1990a, Grace 1993., Kamminga 1982 , Keeley 1980., Semenov 1964)
Pseudo-tools or eoliths, which they can also be called, are the name given to raw materials which has gone through natural processes that make them look like products made by human hand. These natural processes can be wave-activity, water-rolling, glacier transport, rapid temperature changes, internal pressure, tectonic activity etc. All of these processes can cause flakes to detach from a block which looks like an ordinary flake (This concerns rocks that originally have a conhoidal fracture). Other types of raw material might be grounded from sand and wind into “tools”.
- Whittaker, J.C. 1994 Flint knapping: making and understanding stone tools. University of Texas Press, Austin.
- Crabtree, Don E. 1982 An Introduction to Flintworking. Occasional Papers of the Idaho Museum of Natural History 28.