A friend of mine (who is not a fossil collector) found this fossils at the Outer Banks of NC. He asked me what it was (which I told him) and why it had turned from its very black color when found in the sand to brown with a white-ish residue? He put it back into salt water (which I never heard of doing) and it is fading lighter brown. I have had similar trouble with my black fossils that I thought it was salt film and I rubbed olive oil on them and it cleaned it off and made them shiny. But . . . . I don't have any fossils this big and nice and I didn't want to give him bad advice. What is happening to the color and what can be done about it? Thanks for any advice! *This is the fossil below but it is wet and the film doesn't show up unless it is dry.