As a rule of thumb I will seldom buy anything less than 70% silver toned or not but if you're happy with it then that's all that counts. :thumb:
Here's the specs on Mexico's last circulating silver peso coin: Issue began in 1957 and ended in 1967. The portrait is of Morelos the zambo revolutionary who fought in the war of Mexican Independence against Spain. Diameter: 34.5mm; weight 16g; composition .100 silver, .700 copper, .100 nickel, .100 zinc; edge: lettered Independencia Y Libertad. Highest minted year: 1962 - 61,094,000 Lowest minted year: 1965 - 5,004,000
Composition might be listed as 0.100 silver, but this is a silver plating that most I have seen has worn off making them one of the ugliest coins I have ever seen. However the OP coin looks nice.
Actually, there is silver in the composition mix. There is also a silver plating over the coin to give it a nice appeal. Nevertheless your right, when the silver wash is rubbed off over time the coin looks hideous.