6 Pesos Pattern, Tortuga Verde, Iron-Nickel

The Tortuga Verde (Green Turtle) is part of Mexico's long-running Ibero-American series of wildlife patterns, produced as official essays to test metal composition and die performance rather than for circulation. This particular nickel-steel alloy was under evaluation as a cost-reduction measure — iron-nickel compositions were being weighed against the existing bimetallic and stainless alloys used in circulating coinage. Pattern pieces from the Casa de Moneda in this period were struck in extremely limited numbers, distributed almost exclusively to mint officials, central bank archives, and a handful of authorized collectors.