I dont like the texture of the purple gem worth 243 gems.
It appears like it's the same gem shown in the texture of the gem worth 27 gems just from the top.
To make it look more elegant and worthy i would suggest to either add a golden rim to it so it looks like its polished or add an engraving to it as in the coin worth 2187 coins.

An other option would be to change the shape of the last gem or the color of the gems as they progress such as at the coins.
In that process you could even add more stages to merging the gems.

Thank you for this beautiful game!
Best regards :3