Quoted from herg:
I'm going to have to start paying more attention to progress toward diamonds. I find it difficult to follow some of it, even though I've owned the game going on three years. I had a game recently where I had three attempts at melting the witch, finally succeeding on the third try, but I really don't know how many of the other diamonds I collected or how close I may have been on them.
I think it would be cool to have a graphical representation of collected diamonds as part of the high scores list. Even the end-of-game display could benefit from it. I probably just haven't tried hard enough, but it feels like I really have to dig to find the diamond progress, while the witch (emerald) progress is much more obvious to me. I can't even remember off the to of my head whether collected diamonds are shown on the main screen, though I would guess they are.
They are shown on the main screen (middle circle), they are shown at end game if you got 3 or more (on default settings...you can change it to always show), but it would be nice to see the emeralds next to the scores on the high score list as that isn't there.