The C9 I am looking at plays the A string and B strings on the first fret and it looks like the rest of the strings are played open but Im not sure because all of the other chords have o's for open strings not diamonds and yes it is from this site.

It's definately a diamond, I am looking at a C9 variation that doesn't involve barres as I struggle to do them as I have found that I have a little bit of Arthritis in my left index finger that makes it difficult so I need to find different ways to play.

Sorry if I seem to be a total ignoramus but unfortunatley I am  (I have only been playing for a couple of months.)  I know what the X means - that you don't play that string but can anybody please tell me what  the diamond means?