25 Pesos Olympic Games

Mexico's 1968 Summer Olympics were the first held in Latin America, and the organizing committee pushed hard for a circulating commemorative rather than a collector-only issue — hence the .720 silver, a compromise between symbolic precious-metal content and production cost. Tens of millions were struck, which is why survivors are almost universally found heavily worn or cleaned.

The games themselves were overshadowed by the Tlatelolco massacre ten days before the opening ceremony, when the Mexican army fired on student demonstrators in Mexico City. No official acknowledgment appeared on any commemorative issue.