Human made or natural object?

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Human made or natural object?

It often isn't easy to tell of a geological object is natural or has been modified by the hand of humans.

Artifacts are discrete objects which bear some modification from the natural state attributable to humans.

One of the first and basic tasks of archaeology is that of differentiating such human-modified materials from materials that are unaltered from their natural state Alteration may take several forms, resulting in archaeological materials of differing character.
  1. Natural objects may be purposefully modified or moved by man to serve some end. Tools, utensils, and weapons are familiar artifacts of this kind
  2. Natural objects may become modified in physical form as the incidental result of use. The worn surface of a cobble pestle or the dulling of the sharp edge of a stone flake used as a knife represent examples of modification of this kind
  3. The processes of manufacture, preparation or use may result in waste materials which may not be used further but which nevertheless reveal human activity . Flakes removed in shaping a stone tool, the discarded shells of seeds ground for food, the ash remaining from a log burned for heat all represent this form of modification (There is no unanimity in referring to all such materials as artifacts . The term "ecofact" is sometimes used to refer to faunal, floral, or geological specimens modified by human in an ecological context but which lack modification of the first two forms)
  4. Objects may be modified with respect to provenience with or without modification of physical form . This kind of modification is represented by, for example, an otherwise unmodified quartz crystal found in a dead shaman's ceremonial pouch or a river cobble located on a ridge top You will note that specimens of this last kind are identified as artifacts from association or contextual data . This discussion does not consider artifacts of this kind further except to say that their recognition as artifacts requires knowledge of their natural provenience and sensitivity to their spatial relationship to other more readily recognized evidence of human behavior

For several reasons the identification of stone artifacts will pose problems These reasons include the circumstance that many stone artifacts are minimally shaped, the fact that primitive ways of working stone involve processes closely replicated in nature, and the general lack of knowledge concerning the properties of stone and the methods whereby it is worked by humans.

As a first prerequisite, then, it is necessary to become familiar with the nature of stone and the technology of working it. Different types of stones have different properties. Aside from its widespread availability, properties which attracted humans to stone include...

Common abraided stone artifacts

If a stone specimen shows no flake scars, examine it carefully for pecking or grinding marks . Pecking may show up on an otherwise smooth cobble as small, shallow, light-colored pits where the rock was hit with another rock or where it was used to hit another piece . These marks are most likely to occur along or toward edges, but may also occur toward the center
Pecking is chipping the rock from the middle towards the edge and is less precise than flaking

Grinding and polishing are not always easy to detect because smoothing of the rock surface can and does occur through nature  weathering.

Be on the lookout for the following kinds of clues shoulder:

Evidence of shoulders

evidence of a shoulder (edge) where rock has been removed
Profile shows angle or shoulder where curvature of new surface intersects the original outline
shoulder on pestel where rock has been removed
Shoulder (edge) on pestle where rock has been removed

Sharp edge pits

.vesicular(bubbly) rock where grinding is through vesicles
On vesicular rock, the new surface makes sharp angle with exposed vesicles In naturally weathered surfaces exposed vesicles will have rounded edges pit edges rounded

Uneven polish

tools will show areas of polish not even polish
If grinding occurs on an uneven, undulating surface, polish will occur mainly on the high spots even polish

Smooth curved ground surfaces

.in a stone tool a curved surface will be smooth
In a stone tool curved surfaces will be smooth with no protuberances.

The presence of a protrusion on either a convex or concave surface usually indicates that the surface was not used for grinding.

Grinding through grains

ground stone tools will show evidence of grinding through grains
Ground stone tools will show evidence (in crossection) of grinding through grains - this evidence may be microscopic.

In granular or large grained rock, grinding will cut through individual grains to form a smooth surface ; in natural smoothing, this is less likely to occur . (This may not be observable without the use of a lens)

Step by step procedure for determining intentional grinding...

  1. First, feel the clean specimen all over with the fingers for differences in surface texture and sharpness of exposed edges .
  2. Second, hold the specimen up to a strong light and examine it from different angles to see if there are any differences in reflectance .
  3. Examine the specimen by eye, or better yet, with magnifying glass or microscope for striations, looking especially for those that are not randomly distributed but form patterns oriented to the outer borders or along the longitudinal axis .
  4. Hold a straight edge to the surface and observe its contours Most intentionally ground surfaces are either flat or slightly and evenly cured in a convex or concave arc; undulating surfaces should warn caution .