I actually ended up getting new marble, and some slate because the marble that had been cut ended up crumbling. Looking at the two that did not crumble the actual marble veins had been collapsed. The way it was cut was most likely the problem. I bought some new stuff today, and I got marble that has no veins. Talking to Barbie, she said that any marble without a vein will not be a problem for pleco breeding. So I ran with it and got some nice white marble. I'll post pics once the silicone is finished drying.