Just be advised that most of the CSA on
ebay may be/are/could be/perhaps not, forgeries.
How to tell if a CSA is a forgery? I have no idea! Some are marked on the back, most aren't. When it comes to which stone was used, I'm way out of my league. If you are going to spend any big $$, get a cert from a reputable provider and don't get it pre-slabbed!
Just my opinion but, buying a stamp slabbed even with a cert is a "Buyer Be Warned" thing in BIG RED LETTERS. yea, I got burned, once.
I have the 1,2,6,7,9,10,11,12,14 CSA stamps but any or all could be fakes but they all look valid, to me.