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Posted in response to Re: Re: Steve Duggan's photo from Steve Duggan on March 29, 2010 at 08:58:56:

Re: Re: Re: Steve Duggan's photo

Steve, the additional information helps a lot. The black material is probably chert (silica)and the lighter colored rock is probably limestone. This suggests that you have a specimen of fossil feeding traces. The size is about right also. Often chert selectively deposits in areas of higher organic content (worm castings, etc). Acid tests consist of dropping a little acid (any kind, even vinegar) on the rock - if it fizzes the rock is a carbonate, usually limestone. Other carbonates may not give as strong a reaction.

From MikeR - March 29, 2010 at 19:28:31
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