Northwest Argentinean archeoptics: nanotechnology?

In an excavation performed in 1999 at the Campo del Pucara, Alamito site, which belongs to the Condorhuasi Culture (from 0 to 500 AD), and is placed near the frontier of Catamarca and Tucuman provinces in the Northwest of Argentina, Victor Nunez Regueiro and Marta Tartusi Paz found an intriguing archaeological artifact: Remains of a thin slab of schist covered by a mica sheet, dated from 360 and 480 AD. The mica was analyzed by photometric and interferometric procedures and experimental results suggest that it behaves as an interferential dielectric mirror.