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