Although I often answer questions re: costume jewelry, not that I'm an expert, but that I have lots of it and love it, I still recommend:
When it comes to Carats and Karets you need a jeweler. While not every jeweler is a Certified Gem Appraiser, she can be knowledgeable regarding the stone, and the setting. And there are many gorgeous stones that are not diamonds - white topaz comes to mind and so does natural crystal -
Please look further and post back with the results, as all of us jewelry lovers are interested. and ps: Post pics? Thanks and best wishes, KB