Iron-ore mirrors (fig. 251)

Description: Flat pieces of iron ore with one surface polished to a high degree of reflectivity. There are two kinds represented. One (from a San Lorenzo phase deposit) has a concave surface in the interior of the reflecting surface, with convexity on the outer edges. The other mirrors consist of shaped and unshaped small, flat fragments; a few of these are triangular or polyhedral in outline. The Villa Alta examples, most of which are very small, are surely redeposited pieces made in Formative times. San Lorenzo Monument 34 and the ballplayer figurines show that concave mirrors were probably worn suspended as pectorals.

Sample size: 33

Phase assignment: San Lorenzo (7), Nacaste (9), Palangana (2), Villa Alta (15).

Comparative sources: Iron-ore mirrors, especially concave ones, are closely associated with Olmec culture in the later Early Formative and the Middle Formative in much of Mesoamerica. Their manufacture, distribution, and possibly sources of manufacture are discussed in Carlson (n.d.) and Pires-Ferreira (1957).

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GROOVED BARS (figs. 251 and 255)

Description: A small, carefully spaced, rectangular bar of iron ore with a trapezoidal cross section, broken off at one end. A horizontal groove runs across the piece longitudinally at a slight angle; this side is not highly polished, but the sides and the reverse are very well polished. Initial and somewhat crude experiments by Coe established that this object could perform as a compass needle. This hypothesis was confirmed in a far more detailed series of experiments undertaken by John B. Carlson (1975); his conclusion was that this object could very well have served as a north-pointing, geomagnetic instrument. If so, this is the world’s first compass.

Sample size: 1.

Dimensions: 3.4 x .9 x .4 centimeters.

Material: magnetic hematite.

Phase assignment: San Lorenzo