Was wondering what this could be. Unfortunately my kids broke it and I lost the piece that looks like a fossilized oyster or muscle stuck to it I've cleaned it in iron out as I am a collector of minerals but have never found anything like this. It was extremely slimy and stunk when I found it. I picked it up because along bottom has these tiny baby crystals. the copper rusty areas is fragile but has peculiar shapes. Somebody told me it could possibly be a fossilized she'll on coral rock but I'm new to this thank you in advance for any information