Why exactly did the sundrop flower leave behind a dead physical flower after it was consumed by Arianna? Why didn't the flower itself get absorbed with its magic? Could the moonstones magic be separated from the opal, leaving behind a normal gem? Or could that only be done by the sunflower because it was grown BY the sundrop, as opposed to the moonstone, which is the original drop just hardened.
I haven’t really considered it, but I think you hit the nail on the head. The Sundrop was liquid sun that fell to earth and grew a flower that contained its power, while the Moonstone fell to earth like a tiny meteor (I maintain that the splash pattern of the black rocks in the Dark Kingdom with the Moonstone at the epicenter looks like it’s landing place).
Another thing to remember about the Moonstone is that it’s all about that unbreakableness. I don’t think you could break the Opal to get the Moondrop out, even if there was a liquid Moondrop trapped inside there (and I’m not saying there is).