I have a bunch of $10 strikes from the Hard Rock Hotel & Casino in Las Vegas. These are the first issue-type (HR, Mr. Lucky's, Sports Book, The Joint)...both "G" & "S" mint marks. NONE of these are marked ".999 Silver" as most SILVER strikes are (including subsequent issues from the Hard Rock).

The question is: What material(s) are these centers (the rings are brass)?

Thanks for your help.

Steve Bedo