I'm looking for a book, the only problem is I can only remember the cover art, and some of the story itself, not the author or title. I don't mind saying that it's driving me up the wall. So the cover of the book has a flying dragon that's purple and looks like it's made outta crystal or diamond and it's flying over a castle or tower surrounded by green stuff, grass or trees. The bits I remember have golden dragons that shift into human form, a grey drake (kinda demi dragon) in human form with one hand, who has his hand regrown. They end up fighting off an invasion of the crystal/gem dragons. The main character becomes Diamond, god of the good aligned dragons. Also the main bad guy is a crystal who creates a giant body for himself. The main character also is said to have fox like features or is called fox-something. I think it was also part of a series. I read the book in the later half of the 90's... I think. So can anyone help me out? From what I remember it was a good fantasy novel.