I've had a beautiful opal fossilized shell that's from millions of years ago when Australia was a sea in my collection. It's been sitting with a group of things I see every day for 15 years. To my surprise, I discovered that I wanted to create something with it more than I wanted to keep it personally.
I just finished carving the wax. It will be dark (not black) silver with a coral and opal cephalopod (time appropriate). The coral is set with a small ruby and a small emerald.