MEXICO, EMPIRE OF MAXIMILIAN (1864-1867), PESO, 1866, MINT MARK Pi (SAN LUIS POTOSI MINT). Tiny carbon spot in hair to rear of Maximilian's forehead, otherwise well struck, with attractive rainbow toning both obverse and reverse and Very Fine to Good Very Fine (US grade XF45 or perhaps a little better), the rarest date and mint mark combination for this scarce two year type coin (only struck for one year at the San Louis Potosi mint).