PETROGRAPHY OF TUFF FROM QUARRIES ASSOCIATED WITH COPÁN

The classical Mayan ceremonial center of Copán, in western Honduras, was constructed from ash flow tuff of the Padre Miguel group (Miocene) rather than from the limestones used to build other major Mayan cities to the north. Petrographic and chemical analysis of the tuff used for monuments and altars might lead to a better understanding of weathering patterns in these rocks and how further deterioration of these archaeological treasures might be inhibited. We collected samples from areas previously identified as quarries used by the Mayas. Near the ceremonial center, the tuff is green in color due to zeolites and a high clay content. Tuff exposed in road cuts and quarries to the east and west ranges from white to coral pink in color. A mafic dike that intrudes the tuff near the west edge of the ancient quarry northwest of the ceremonial center may be responsible for the hydrothermal alteration that has made this tuff unlike any reported elsewhere in Honduras. The high clay content softens the rock when wet, making it easy to cut into the elaborate sculptures for which Copán is famous. Repeated cycles of wetting and drying, however, cause these rocks to disintegrate due to stresses associated with shrinking and swelling. Laborers who currently produce blocks of tuff for construction in the Copán valley probably use tools and methods like those employed by their Mayan ancestors. Levers and wedges are used to separate jointed blocks from the quarry face, and a single blow from a heavy hammer is often sufficient to split a block at right angles to an existing face.