I''m nowhere near being an expert, and definetly not brilliant, but my best "just for fun" guess without knowing any other measurements is between 0.6 to 0.8 carat. If it''s cut very shallow or very deep or has weight hidden anywhere (like in a very thick girdle for example) that would make a difference in the spread as well. With an average table and depth, my guess is 0.65 carat. Do I win a prize?
I'd say .60 - .65 ct. but I could be wrong because we're lacking depth. I just saw an antique EC (Blueroses') that faced up near what you would expect a full ct. to face up as, but it was only .62 ct.