As I do pretty much every day, I just went to Circle K (a gas station / convenience store) for Polar Pops (the Polar Pop Diet Pepsi over just a little cubed ice: a necessity of life). My change consisted of three quarters. When the clerk handed them to me, they sounded different — more, well, clinky than usual. Higher-pitched.
Upon examination, I found that one of the three quarters is dated 1961. It’s a lighter silver color that the other two quarters, and from the side it’s all silver instead of silver/copper. When I drop it onto the table, the note it plays is a third higher than that produced by the newer coins. (Not a music geek? Think the notes of “three” and “mice” in “three blind mice.”)
Someone numismatic expert, please save me from figuring out the right search terms for Google, and explain the difference.