I have a few Mexico 1948 5 Pesos coins, but I noticed on this particular example there is extra metal at the chin and the last feather in the headdress. Can anyone explain what this is called or why it happened? Does it add any value? Thanks.
"Extra bits of metal" that appear to be stuck onto a coin are caused by small pieces of the die, which was used to strike the coin, breaking off. They are therefore called "die chips". Die chips that occur at the rim of the coin are called "die cuds".
They add a little extra interest for variety hunters, though it does depend to a large degree on the quality control at the mint in question. Mexico was still pretty good back in the 1940s, so die chips aren't too common. Still, for "added value", you need there to be a lot of die-variety collectors, and sorry, I wouldn't know about that.
Maybe with a bit of marketing spin, you might get a few extra dollars for it. The "Bearded Aztec variety", anyone?
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis