So I just returned from a vacation to the Canadian Rockies and I picked up a few nifty locally-grown things there. Has anyone heard of "ammolite"? It appears to be fossilized ammonites that aquired an amazing iridescence all over the surface somewhere in the process. Reds, greens, yellow, blue, purples. Reminds me of the most firey opal i've ever seen. I picked up a small chunk. It's just a millimeter or so of it on a base of limonite, quite fragile. Usually they protect it with a clear coating or (for jewelry) with a spinel cap. Pictures soon to follow.