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The Organization of Chipped-Stone Economies at Piedras Negras ...

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from Ixtepeque, the opaque black corresponded to Zaragoza, and the grainy clear m<strong>at</strong>erial<br />

containing black fleck inclusions represented the San Martín Jilotepeque source. <strong>The</strong><br />

second round <strong>of</strong> XRF resulted in an 80% success r<strong>at</strong>e for the pieces tested. Nine <strong>of</strong> the<br />

fourteen visual c<strong>at</strong>egories were correctly determined to be El Chayal and two others<br />

represented the Ixtepeque and Zaragoza sources. <strong>The</strong> three remaining c<strong>at</strong>egories were all<br />

some grad<strong>at</strong>ion <strong>of</strong> grainy, clear-to-grey obsidian th<strong>at</strong> could not be identified as San<br />

Martín Jilotepeque or El Chayal with complete certainty. Because this ambiguous<br />

obsidian, which confounds a visual determin<strong>at</strong>ion <strong>of</strong> some kinds <strong>of</strong> San Martín<br />

Jilotepeque obsidian, made up such a small fraction <strong>of</strong> all obsidian <strong>at</strong> <strong>Piedras</strong> <strong>Negras</strong><br />

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