Kind of looks like the Nirvana chalice. Do you know where it came from? It can develop a purple rim under lower light and a green rim under higher light.
thats the closest thing i have seen to it yet.i got it when i bought a bunch of frags and equipment from a local reefer getting out.the frag was about the size of a dime and all brown i just left it in my frag tank and this is what got.it is under high light now i was thinking of moving it to my display soon where it will be on the sand.