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another discoidal rock / grinder
This is a Diquis artifact from Guerra on the Rio Sierpe in southwestern Costa Rica; borrowed for this show-and-tell. It was made by pecking and then grinding from gabbro, the same material as the stone spheres. This stone comes from the Rio Terraba (to the north), so it was imported (as was the case with the spheres).
It is 6 to 6 1/2" in diameter, and 2 to 2 1/2" thick. The dimple depressions are on both sides, slightly off center and not aligned, and ~5/8" deep; the picking pock marks are clearly visible in the center. The sides, including rounded outer rim and central depression, are ground smooth; pecking is faintly apparent at the outermost periphery.
An identical piece is pictured in an older book on CR archaeology, and google shows pictures of similar ones called 'grinders' - no idea how such was concluded. Many questions, no answers. (not a nutter, chunky gaming disc, etc.)
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Sorry about the images, learning.
Bill
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and another discoidal grinder
another discoidal grinder based on the wear patterns, ~4" dia
the pecking in the centers and edges is clear
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as are the beveled edges of old fractures, hence the use of the word grinder
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the previous one from a non-local stone, and this one from the adjacent river
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